SectionHiker.com Backpacking Gear Reviews and FAQs 
Ventilated backpacks have suspended mesh back panels to help dry perspiration when you’re carrying a backpack. The mesh is suspended above a concave cavity so there’s a big air space behind your back to help evaporate moisture. Deuter Packs, which is still the largest backpack manufacturer in the world, is credited with inventing ventilated backpacks, or trampoline frames, as they’re sometimes called. Since then, Osprey has emerged as the biggest producer of ventilated backpacks, as well as REI and Gregory.
But how effective are ventilated backpacks at preventing sweat or drying your shirt more quickly? Besides anecdotal evidence that people “feel cooler,” is there any evidence that people burn fewer calories when they carry a ventilated backpack, or that they need to hydrate less, or some other measurable benefit?
It’s not an outrageous question to ask because there are pros as well as cons to carrying a ventilated backpack. For example, some ventilated packs pull you backward and off-balance because they have such large air cavities behind the mesh. This can actually make you burn more calories, to compensate against the forces pulling you backwards. The same concave intrusions make it more difficult to pack ventilated backpacks efficiently, carry hard-sided bear canisters with them, or find gear buried deep in your pack.
Deuter, to their credit, commissioned a study with the Hohenstein Institute, a test laboratory, and research institute, to quantify the benefit that ventilated backpacks. They found that the three-way mesh ventilation system in Deuter’s packs “reduces perspiration by 25%.”
That doesn’t sound like much, but it could add up to a considerable weight savings in the amount of water you needed to carry in an arid environment where you have to carry a large amount of extra water. For example, if you needed to carry 8 liters of water with a non-ventilated pack, you would only need to carry 6 liters with a ventilated one. That’s a weight saving of 4.4 lbs, which is not insignificant.
But how often do you have to do a long water carry where you hike? I rarely carry more than 2 liters and often carry less.
How do you rationalize ventilated backpacks?
Philip, I agree. Water weight is not much of a concern. (I carry 1 litter at the start of a trip, ~2pounds.) Ventilation? Well, again, I rarely hike in open areas. I have been out with my legs and arms numb from cold yet still perspire hiking. And I don’t se any benefit to the pivot back caused by air spaces between me and my pack, though this is more about using your ankles to hold your body angle correctly for balance. In hot, open terrain like the dry prairies or desert like areas of the western areas, perspiration is inevitable. You actually want something to hold it against your body and wick it to other areas cooling them. I don’t see where this is a big deal. HYOH.
I find the comfort and packability of my HMG 3400 southwest way more comfortable than the Osprey Ather 70 that i started with. breathability of the osprey is better, but the HMG feels much less bulky and i can pack way more into the bag. that said, your back is going to sweat with either. On the long flat stretches i release my shoulder straps some to give distance and vent, this works great! HMG has the best and most comfortable waist belt and allows me to loosen shoulder strap without penalty. I feel the closer the pack the more you become one with, as opposed to accessory hanging off you.
Yes – I’ve tried on a couple of Ospreys in the store and they feel rigid, unbalanced and unnatural compared to a more compact internal frame like the HMG. With the trampoline designs, I feel like you pay a high price in wearability in return for a modest gain in ventilation.
I have an Osprey Atmos AG 50. I can’t quantify these observations, but in the summer, hiking with a tshirt, my back “feels” more comfortable, and my shirt “seems” to be drier. When I am wearing a shell, I certainly notice that my shell seems to be able to breathe more effectively without the pack right up against my back. I have not noticed that I feel off balance wearing it, but my loads in the pack rarely exceed 25 pounds. It wouldn’t be my first choice for climbing or mountaineering, though, because of the potential for this to happen.
I bought the Thunder Exped, largely based on your review, and find that the large gap between the shoulder pad and the hip belt allows for good ventilation without pushing the load too far out from the body. The pack is pretty much a straight cylinder, very easy to load. My main trip last year was to Philmont, New Mexico, and my back never felt sweatier than the rest of my body.
I don’t really rationalize ventilated backpacks these days, in part thanks to your website. My first large backpack purchase was an Osprey Aether 60, and when it’s loaded you don’t really notice the sweat savings and it does put me off-balance if I step wrong. My two newest packs, both for day hiking and backpacking are not ventilated.
I would add that my large day pack I’ve been using for 7 years, Millet Elevation 40, is ventilated with a really curved framesheet. I think there could be an advantage using a ventilated day pack for big hikes, since you probably won’t have enough weight to throw off your balance. But I don’t think I’ll ever buy a ventilated pack again for backpacking.
Wait a minute, did the Deuter research indicate that the “25%” referred to total body perspiration, or just on the area of your back that contacts the pack? I find the former to be extremely unlikely, you simply don’t lose that much heat through your back, irrespective of covering.
They don’t elaborate, but I would imagine it’s total body perspiration because that might be measurable.
Seems like you sweat just as much but your shirt would just dry off faster with a vented mesh pack.
Exactly. The amount of sweat really depends on the cooling efficiency of the sweat as well as the level of exertion (amount of heat the body needs to shed to keep homeostasis). The air circulation you get with a vented pack doesn’t compare with a good rest/sock change/hydration/eating break with pack off and shirt off/loosened. And you need the rest etc break anyway.
Interpretation of Osprey’s stats depends very much on the temperature and relative humidity of the test site. Nothing’s going to help when the temperature is 90 F and humidity is 80 or 90%. Keep drinking water (with added lytes or food) and sweating, that’s all you can do.
Philip, reducing perspiration by 25% is not the same as reducing water consumption by 25%. Respiration and metabolism also consume water. Depending on the circumstances I would guess that perspiration accounts for 25-75% of water loss. But as a frequent desert hiker, I find even that reduced fraction to be significant.
Metabolism produces water, it doesn’t consume it.
If it’s not ventilated, I won’t even consider it ! Sure, if it’s hot out, your whole body sweats either way. But if it’s cold out, your back will still sweat with a non-ventilated pack. That’s when you notice the difference. NO SWEATBACK PACKS !
I like the added insulation that the backpack offers in cold weather. Even better in winter, I can feel my bottles of hot water radiating heat through the back panel.
In winter, it may depend on getting your layering system dialed in. I started hiking the Whites this past winter, and with the wide differences in temperature or strenuousness of the hikes, I almost always wound up soaked, then spending minimal time above treeline freezing, then changing layers when we got back down in the trees. On one hike up Moosilauke, my shell literally froze solid it was so wet. Now, I just turned 58 and have to keep up with two teenage boys, so that’s probably part of it. But the (likely) last hike of the winter up Mt Jackson on Monday I felt like I had my layering selection going well, but at the end my back was still soaked from perspiration under the pack, and it has several deep channels.
I’m seriously thinking of picking up a Gregory Optic 58 that Philip recently reviewed here shortly…
Steve – I’ve found that perspiration is inevitable. In winter, I typically wear a base layer and a mid-layer fleece. The base layer wicks all the moisture to the mid-layer, so I never feel wet. I typically take my shell off when climbing to reduce perspiration too.
Me, too- but the back was still soaked this last trip. It was a short hike or I would have changed out my fleece mid layer before descending…
Philip – you might want to check out and review the Brynje style string vest base layer system, if you haven’t already. Developed in Scandinavia for severe conditions you cap it with a conventional base layer and it traps an insulating pocket of air against the skin. This helps keep you comfortable and reduces heat loss when clothing gets wet. It also also prevents the dangerous flash cooling you can experience when you have to stop in cold weather or if you get soaked for any reason.
This system is widely used in Scandinavia and by Arctic specialists. It was also used by Hillary on Everest. I find it works very well, and reduces the nuisance of a sweaty back from my unventilated pack.
(It has advantages in summer as well, when it can help with cooling when you vent your base-layer. It’s widely used by elite road cyclists, for example)
I’ve already reviewed them. Wonderful stuff.
I have an old Deuter Race X Air 1 bike/hydration daypack I’ve used for years. The curved design holds less than other packs (850 cubic inches of space isn’t bad, though, and I don’t use the bladder that comes with it), and does so less conveniently, but it makes up for that for me by being so comfortable. It’s actually a delightful feeling when a breeze hits your back!
I have not seen the study but that statement could mean two different thing
1). That the sweat that your body moves out thru the skin is 25% less Or. 2) they the perspiration accumulation on your shirt is 25% less (same sweat output but better evaporation and less accumulation). #2 increases comfort and less soggy shirt syndrome but has no impact on water consumption
There is no study. Just that quoted content.
okay, thanks for responding
Now we can sit back and watch Backpacker magazine turn this into many “exciting articles” about the ventilated pack revolution. I think they can milk this for several years.
The people with the most interest in this topic would be the US military. I know they move slow but they have been in the middle east a long time. Until I hear from them, it is a comfort and taste issue. A great fitting backpack w/o ventilation is still a great backpack. A poor fitting or poorly designed backpack won’t be saved by adding ventilation.
Still, the whole thing has been an interesting conversation to watch and the article is a great review of the development and variety of ventilated backpacks. And after all, that was what you set out to do. Thanks
I realize it’s a personal taste thing and I’m ok with that. I just think it’s interesting that there’s so little scientific justification for it. Nothing, except Backpacker Magazine sponsored hype and Americans’ pre-occupation with cleanliness.
My Arc Haul just plain feels good with the mesh backing. I used the Mariposa for years on the PCT and AT and now prefer the Arc Haul … in part due to the air circulation on my back.
Same here. I’ve used a few different Osprey and Deuter models but have stuck with the Arc Haul for the last couple years. It’s also nice that you can adjust the amount of bend in the arc.
The only issue I infrequently have is in the Winter when I have to carry additional gear/clothing. The design of the frame sometimes will not allow me to create the arc if I have the bag packed to the brim.
Since we are talking about ventilated vs non-ventilated backpacks, I have been kicking the tires on a SWD Long Haul 50L. I know you reviewed it somewhat recently. It looks like it is just X-Pac material on the back panel with none of the somewhat absorbent padding seen in most non-ventilated packs (ie ULA). Does this make it a hotter pack compared to other non-ventilated packs?
I don’t think there’s much difference if it’s touching your back. Those padded backs don’t really breath all that well.
I own five Deuter packs and a Zpacks Arc Haul Zip. I appreciate that they ventilate without relying on an exaggerated arch (i.e. Osprey style). In fact, I don’t arch the frame of my Zpacks at all, the trampoline still provides air space. Deuter’s systems are all highly effective as well. I carry the Zpacks these days because it’s so light and comfortable. But I’ll never part with my Deuters… they’re companions with whom I’ve shared wonderful adventures. Without sweating too much :)
I’ve used my Flash 45 on three trips so far with no perspiration, but it was in the winter so I don’t know if the mesh made a difference. I can say it is by far the most comfortable pack I have ever used.
I bought an Osprey Exos 48L because it was on sale and I imagined it was going to be the solution to sweaty back syndrome. Alas, even at 40* temps with only a long sleeve button up shirt on, my back still ended up sweaty.
That to say, for some people, you are going to get sweaty no matter what. Glad I only spent $100 to figure it out.
I think Leonidas is exactly right; sweat proclivity seems to vary a lot among individuals.
Not sure what Deuter is about with their “inventing ventilating backpacks” (in the 1980s, i believe). Maybe for internal frame packs. My old Kelty Tioga external frame pack from the early 70s had a wide, mesh band across the lower back. The updated Super Tioga which i still sometimes use for longer, three-season hikes (yeah, go ahead and laugh) has the same design.
That mesh keep most of the pack about two inches off my back. In warm weather (70s and up), when i’m hoofing up a hill, wearing just a t-shirt and shorts, after a couple of hours, my shirt is soaked from sweat. The sweat drips down and soaks the waist belt, and the shoulder straps are mostly saturated, too.
So i can’t image minor variations in these mesh-based designs would make much of a difference for us open-pore types.
Where I hike water is plentiful so there is no problem carrying that extra weight however in summer when the thermometer reaches 28 deg C plus and humidity is high, 65 plus I find that the ventilated back make for much more comfort along the trail especially the long climbs. Anything that alleviates excess sweat decreases “Trail Stink”
Conditions are different all over.
On hot days, loose (ventilated) packs do well. So do cotton T shirts.
Historically, typical desert wear is a longish cotton poncho allowing sun protection & ventilation, and, allowing sweat to penetrate and wick around the garment for cooling and to hold humidity next to your skin. Bags and single strapped carriers are used. This reduces overall sweating, reducing water consumption. It has worked for thousands of years in the middle east, and other areas where water is in limited supply.
On the other end of the scale are cold conditions where retaining heat is more important than shedding it. Tighter packs fitted closely to your back do better holding heat. Again, this has worked through most of history as one means of hauling gear and examples can be found back to the Neanderthals.
So, ventilated backs with backpacks is hardly a new idea regardless of the hype. Water weight is…well, water weight. You carry what you need or you go thirsty. This is a biological necessity that cannot be avoided. You have to find sources as you hike, or, you go without. Sweat is one way your body can regulate it allowing your body to increase in heat while shutting down perspiration. You get a rather high fever, feel sick, and generally do not do well without water. Even in colder climates your body knows how to shut off perspiration often leading to dry, chapped, skin, reduced cognitive skills, and other dehydration problems.
Ignoring water weight, because you need to carry or find what you need, comfort is usually defined by how comfortable your body is. We worry about the minor details in temperate climates because there is no one good solution. We hike up a mountain and get hot and sweaty. We hike down the other side and get cold. We have both sides of the heat problem. To me, it is a wash. It doesn’t really matter.
We see Z-Packs producing some nice UL trampoline framed packs, they are in Florida. We see MLD producing some nice no-framed packs in VA and HMG producing some nice stayed packs in Maine. It kind’a depends on how you apply their packs (just to name a few,) but all are good packs. All have different design priorities.
As Philip says, just use the pack to get out. The actual design only matters when you 1) establish an area you hike, 2) establish a set of goals within that area, and 3) establish a system based approach to each goal. Traveling will change this, moving will change this, expeditions will change this. Hiking is not usually THE end point.
I rationalize my Atmos 50 AG because I needed an upgrade and got last years model on sale for $130. Love it. First trip out I felt like a bottle was leaking in my pack but it was the ventilation drying/cooling the perspiration off my back. And it fits like a glove with excellent weight distribution. Thanks for all your product reviews, Phil. They help us out immensely!
My husband and I purchased Deuter 36 and 34 litter ventilated packs with the “trampoline” a couple years ago to hike 12 days doing the Haute Route to Zermatt. We only were carrying approx 25 lbs. We loved our packs for this trip and felt they did keep us cooler. We also felt the pack was part of our body, very comfortable and never did we feel off balance or feel any shifting. We normally hike with bigger unventilated packs and much more weight and perspired a lot more. I thank you all for your input. We will consider this as we were thinking of getting new large back packs that were ventilated but it might not be worth cost or comfort based on some of your comments.
Last summer I got a horrible skin rash from hiking Pa & Md in July with a non ventilated pack. High 90’s brutally high humidity. 5-6 liter days plus more in camp. I washed the sweat out of my shirt every day, several times most days. And wore a different super clean shirt in camp and for sleeping. But still got a square foot of “spinal monkey butt” that really sucked. Tried the one shoulder carry (6.9 base at) and even tucking the pack under one arm. Sucked so bad I forgot to hate the rocks.
Bought an Eos 48 at Delaware Water Gap and voila no more SMB. Have had zero luck with “wicking” fabrics next to the trampoline mesh but “vented” shirts with little holes are awesome and no shirt at all is double awesome, at least for ventilation.
Not in love with the Eos though all my stuff plus ten days food only fills it half way up and the compression straps don’t make the pack smaller in a way that works for me it just turns into a lumpy old potato sack.
Not sure if anyone on earth but me has had SMB but me, but I don’t recommend getting it on trail.
Mine is dry and scaly. I found that a little Eucerin Lotion clears it right up. Only happens during very very humid summers.
I typically hike in MD and VA – where the temps and humidity are both in the 90’s.
Will the Exos or Aether (AG?) keep the sweat from running down my back and soaking my underwear any better than packs with 3D mesh back panels ? What’s the best 40-50 liter pack for summertime ventilation ? What’s the best ventilated pack that doesn’t pull off-balance or sway on steep rocky sections of trail or scrambles ?
3-D mesh is really warm- stop for lunch in the winter and you feel the loss of insulation right away. It can turn into a sponge in certain conditions, specifically an open cell sponge that drains “you know where”.
Human skin is designed/evolved to sweat: the problems come from soggy clothing, salt, and rubbing. No one thing is going to be a miracle cure it those conditions; here’s some things that do help:
1) soak your shirt it will cool you better than sweating
2) stop wearing underwear
3) take your shirt off on uphills and shady sections
4) plan your day around the heat instead of through the heat
5) try Bikram hot yoga to get better used to exercising in the heat.
6) splash or dunk your head in cold water when you can.
Try carrying a woven basket on your head naked. No, seriously. Nothing you do will make any difference in this conditions.
“Nothing will make any difference…” Except designing your day around the conditions, as Groundhog suggests.
When it gets really hot I do more night walking. Can be a delight when there’s a good moon. On PCT vlogs, for example, you often seem people toiling up exposed slopes in blazing heat when they’d have been much better off in the early morning or the evening. Kit can only take you so far – sometimes you just need to make smarter decisions.
(You also see people postholing on warm afternoons when they could have made an alpine start and passed through on crisp snow, but that’s another topic…)
I have been using the Exos 38 since March last year. It has been my go to day pack in that time. The only thing I would change is to make both lids removable to make it more versatile and make the hip fin pockets larger. The frame works well and you can feel the air passing over your back when hiking. Out in the snow and ice last winter I fell flat on my back several times. Thanks to this back system I was uninjured and the pack shows no sign of damage.
First off, pack fit trumps everything else. If carrying the weight you need is painful, no amount of sweating or not sweating will help.
I’ve used both ventilated and unventilated packs over many decades, and … pack fit trumps everything else. Right now, I love my HMG Windrider unventilated pack, even on hot, muggy days. Ventilated or unventilated, hot or cold, dry or muggy, I still sweat prodigiously.
And like Nick in Mass said, ventilated frame packs have been around since at least the early 1970s. My old Trailwise pack had a full-length mesh panel.
I have a ventilated backpack that sits away from my back. I carry anywhere from 40-70 pounds because I’m often packing for two. More so than the ventilation, the stiff frame sitting away from my back puts less pressure on my shoulders. The difference in fatique has been night and day different for me. The benefits of having the hard frame have allowed me to stay out longer and not feel decimated at the end of the day.
Yes, I find the same. I will take a heavier pack with the hard frame any day for the reasons you mention. The only think I don’t like about my Osprey is that I find it’s harder to pack because of the curve.
It’s like you guys never heard of evaporative cooling.
Where I live it is hot and dry. We want to sweat, because that sweat will evaporate and cool us down. Botijos here turn 30°C water to 5°C water in about half an hour. Simply wrapping a wet T-shirt around a beer bottle pulls about 15°C out of it in the same amount of time. And it doesn’t matter if the water is hot or cold. The process functions in much the same way.
When you can’t sweat enough here you splash water on wrists, behind ears, on ankles, behind knees , back of neck etc. Then it evaporates and cools you down. And it doesn’t matter if the water is hot or cold. The process functions much in the same way.
How much you sweat is a factor… but how effective your sweat is at achieving its evolutionary purpose of evaporative cooling depends on how much air can flow over it and how dry the atmosphere is.
No gap between my back and my pack = 0% evaporative cooling
As with most gear issues, it seems to be a question of tradeoffs. Full venting helps with evaporative cooling in hot conditions, but the more rigid frame and the gap has a negative impact on balance and walking ergonomics. Conventional against-the-back internal frames are more flexible, keep the weight closer to the body and are warmer in winter, but can contribute to overheating when it’s hot.
On short hikes in stable weather I guess you can just select the right pack for the conditions if budget allows. But on longer hikes or in changeable weather it’s more of an issue.
One solution might be a back design that was adaptable. For example I think that McHale offers removable lumbar and scapular pads that would increase venting when used, though I suspect that they aren’t really designed to be adjusted on the trail. Can the Arc packs be quickly adjusted to ride close to the back, or do most people simply keep a standard gap in practice?
An alternative is a compromise that’s designed to allow some additional venting while keeping the load close to the back, using spacer mesh for example. My current pack has this, and combined with loosening the straps for some venting when on easy ground, this works tolerably well in the heat. I certainly prefer this to the Osprey designs, which I find uncomfortably rigid.
I make my own gear, so if anyone has any ideas for something adaptable, it would be interesting to work up a prototype.
One relatively new and innovative solution to the market is VENTAPAK. It is an external frame (frame + mesh + attachment clips and buckles) that attaches to backpacks to create major separation between a person’s back and their backpack. I find it more comfortable with much more airflow and sweat reduction on my Swiss Ruigor backpack than an expensive backpack – $180 – that I bought with an internal frame but not much airflow – collapses down into my bike especially when biking. It has gotten positive reviews from the media and customers and is good to know about.
For daypacks maybe.
The Vaucluse Gear (I have no affiliation) Gen 2 ultralight backpack venitlation frame is interesting since they advertise fitment for 15L-55L backpacks. At 3.3oz and currenlty 42% off if you buy two during pre-order, it seems worth checking out. The Gen 1 seems to have gotten fairly good reviews, and I’m hoping good things when I get my Gen 2, because I’ve been looking at some sort of mesh trampoline or vent system like zpacks integrates to put on my HMG packs.
Just bought a gen2 to try.
Somewhat paradoxically, I find ventilation most critical in winter. I can snowshoe up even at 15°F in nothing but a t-shirt and still get a wet back. That then becomes dangerous. The wet back only comes from my pack touching my back and not allowing ventilation. So I find this ventilation is critical in these conditions.
It’s only dangerous when you stop. That’s where a wicking layer like a fleece comes in handy because it will move the moisture off your skin. But yeah, a ventilated pack could conceivably help you. Personally, I prefer the added insulation of a backpack close to my back, particularly in cold wind.
I find the wicking layer oversold. The wicking layer is only as good as the non-wicking layer ability to dissipate moisure. In an optimal scenario, the wicking layer will pull moisture from the skin, onto the outer fabric laye for dissipation, but even then if you saturate your sure because you are a sweaty little pig like me, wicking isn’t doing anything. There isn’t any wicking material out there that will keep you dry if the drying conditions limit evaporation, which is the environment created between the backpack and the clothes on your back.
“Deuter, to their credit, commissioned a study with the Hohenstein Institute, a test laboratory, and research institute, to quantify the benefit that ventilated backpacks. They found that the three-way mesh ventilation system in Deuter’s packs “reduces perspiration by 25%.””
Any chance you could link to this study? I’d be interested to find out more! Many thanks in advance :)
Not available. I tried.
I’m pretty sure Hohenstein would have come to the same conclusion about ventilation space regardless of Deuter Aircomfort. You can websearch for Bed-Mead-Smaller pdf from Hohenstein which goes into their testing methods, clthing physiology, etc.
I found out two important things when hiking became part of my life… I generate a lot of heat and getting hit with a blast of cold air against a wet back sucks. For those reasons I bought a Gregory Citro and the quality of my life on the trail became instantly better.
So while I enjoyed the article (as always) and acknowledge the points about packing considerations, calories & hydration, sometimes it just boils down to comfort. I am much drier with this pack and I will probably look for ventilated mesh in my next one.
I’m a little puzzled by some comments. Yes, in hot, humid conditions one will sweat. And yes, that will result in evaporative cooling where air can reach the sweaty areas. All well and good.
But with a pack that fits tight against your back, there is no way for the sweat in that area to evaporate. Most of your shirt may be be essentially “dry” as your sweat evaporates, but take off your pack and your back and the foam backpanel are soaked. Nothing is more uncomfortable than a wet back and having to put that soggy, cold pack back in place after a break.
I kept going back to my Tioga for years before internal packs “discovered” ventilated mesh, and now find that the ventilated mesh on my Atmos and Stratos are the one thing that makes internal frames finally enjoyable. I won’t say that I don’t sweat on really hot days, but my back is not much worse than the rest of me.
I think there are plenty of scenarios where you have to carry lots of water. I think North American thru hikers are a bit spoiled in that there are trail angels and artificial water caches along the hiking routes, which allow for minized water carry requirements. In other areas, that is definitely not the case. I been on two such backpacking trips recently: one in the Australian outback and the other in the Gobi Desert. Natural water sources and civilization water sources are few and far between, so you are carrying a lot of water. Combine that with the aridity, you need to consume fare more water than you think you need to consume. On the opposite end of the spectrum, in high relative humidity environments you are both drinking a lot and your wicking fabric isn’t going to keep up with the environment, even if you take frequent breaks.
Ventilated packs objectively work when relative humidity allows evaporation.
The subjective part may depend on the clothing worn under the pack. If sweat can evaporate either directly off your back or indirectly off your shirt/layers, then you will experience a cooling effect. If not, then you won’t.
An extreme example is when you wear a rain jacket under the pack. In that case, you will mostly feel the rain jacket pressed against your back. It will feel similar regardless of whether the pack is ventilated.