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Katabatic Gear Flex 40 Quilt Style Sleeping Bag Review

The Katabatic Gear Flex 40 quilt-style sleeping bag comes with a sleeping pad attachment system

The Katabatic Gear Flex 40 is a premium quilt-style sleeping bag. Weighing 16.9 ounces (18.2 actual tested), it’s filled with 900 fill power goose down and comes with an effective sleeping pad attachment system to help prevent drafts from blowing under the edges of the quilt when you move around at night. Katabatic Flex quilts (available at multiple temperature ratings) also come with draft collars that snug around your neck and prevent heat from escaping when you move. The Flex footbox can be zippered closed and has a drawstring vent, which is convenient for temperature regulation as your body cools at night. Finally, you can also unzip the Flex fully and use it as a blanket in warmer weather – hence the name Flex, because this quilt has a chameleon of uses.

Katabatic Gear Flex 40 Quilt


First Rate

Katabatic Gear Flex 40 Quilt is a beautifully crafted top quilt that includes an innovative pad attachment system to keep you on your sleeping pad at night. A draft collar and zippered foot box help you control your warmth level across a wide range of temperatures.

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Specs at a Glance

  • Weight: 16.9 ounces (18.2 ounces actual tested)
  • Dimensions: 72″ long x 54″ shoulders x 47″ hip x 40″ foot
  • Insulation: 900 fill power goose down, responsibly sourced
  • Down Fill Weight: 8.5 oz
  • Shell: Pertex Quantum
  • Click to for full specs and options at Katabatic Gear
The Flex 40 can be opened up like a blanket for warm weather.
The Flex 40 can be opened up like a blanket for warm weather.

Draft Collar

A draft collar is a fabric tube filled with down insulation at the top of a quilt or sleeping bag that wraps around the upper chest and neck to prevent warm air from escaping at night when you move (the so-called bellows effect).  It’s frequently found on winter sleeping bags but has started to crop up more widely on ultralight sleeping quilts, including the Flex 40. It’s a fabulous feature, especially when you’re trying to “push” the warmth of your sleep insulation below its minimum temperature rating.

The Katabatic Gear Flex 40 has a down filled draft collar
The Katabatic Gear Flex 40 has a down-filled draft collar

The top of the Flex 40 closes with a flat plastic snap behind your neck. Don’t worry, you can’t feel it. When you pull on the drawstring that tightens the neck closure, the draft collar conforms to your shoulders and neck. I consider a draft collar a must-have feature on a backpacking quilt and you’ll become a convert too if you get one.

Vented Foot Box

A vented footbox is a useful convenience on a warm-weather quilt because it lets you regulate its warmth: when you go to sleep after dinner and your metabolism is running hot, you can vent the footbox to let off extra heat and easily close it later at night when your metabolism is less active or the external temperature drops.

The vented footbox is formed by snapping closed the quilt end. The bottom draft tube can be stuffed into the holes on either side of the snap and ones created by closing the drawcord to block drafts.
The vented footbox is formed by snapping closed the quilt end. The bottom draft tube can be stuffed into the holes on either side of the snap and ones created by closing the drawcord to block drafts.

A snap at the base of the Flex gathers the sides of the quilt together to form a footbox, while a drawstring that lets you adjust the size of the opening. The problem with a drawstring footbox closure is that you can still have gaps in it.  Katabatic addresses this with a short draft tube that runs below the snap and can be stuffed into the gaps formed by the drawstring.

A small zipper helps extend the footbox higher up your legs
A small zipper helps extend the footbox higher up your legs

A rear zipper on the underside of the quilt extends the footbox higher up your legs. It has a tendency to catch on the quilt’s shell fabric when zipped or unzipped. Just be careful when using it.

Sleeping Pad Attachment System

One of the things that distinguishes Katabatic Gear from other UL quilt manufacturers is the quality of their sleeping pad attachment system. It’s simple but effective at keeping the quilt wrapped around your body when you roll over at night.

The Flex has two sets of clips sewn to the inside edges of the quilt that lock into cords you wrap around your sleeping pad. The clips have two positions: one that controls the girth of the quilt and how much internal airspace you want and the other that locks the quilt in position. The attachment system works best with sleeping pads that have firmer edges like a self-inflating Thermarest Prolite pad, a foam Zlite pad, or a NeoAir Inflatable pad. Pads that have flexible edges like the Klymit Inertia can collapse when you roll over creating too much slack in the cord system to keep the quilt on you.

Do you need a sleeping pad attachment system for a quilt? Is using a cord based one, really worth the extra hassle of configuring it and clipping in and out whenever you need to get up at night. I think these are both debatable points. Big Agnes or Therm-a-rest style sleeve-based systems are arguably more effective and easier for most people to use without much weight penalty.

There’s also less of a need for a pad attachment system if you sleep in an ultralight bivy sack which tends to hold a quilt in place, even if it’s not quite as efficient at heat retention. Some people also dislike feeling confined by a sleeping bag attachment system, which can be a step down from a full zip quilt-style sleeping bag like the Feathered Friends Flicker 40 or the Enlightened Equipment Convert in terms of comfort and convenience. Net, net. While Katabatic Gear’s sleep attachment system is good, consider whether you’ll actually use it in the context of your entire sleep system and how essential it really is in the weather conditions you plan to camp in.


How does the Flex 40 stack up against comparable quilt-style sleeping bags than can be fully opened like a blanket from other manufacturers? Here are three slightly different alternatives, although I’m sure there are others I’ve missed.

  • The Feathered Friends Flicker 40 UL weighs about 1.8 ounces more (20 ounces) than the Flex 40 but is filled with 8.4 ounces 950 fill power down. It has a draft collar around the neck and a vented foot box. It doesn’t require a sleeping pad attachment system because it fully encloses the sleeper like a sleeping bag, with a full-length zipper backed by a puffy down-filled draft tube.
  • An Enlightened Equipment Convert 40 (14.29 ounces) is significantly lighter weight overall than the Flex 40, but lacks a draft collar around the neck. It also has 7.11 ounces of 900 fill power down (based on the manufacturer’s temperature ratings and a 72″ x 54″ sizing equivalent to the KB Flex 40. ) Like the Flicker 40, the Convert is a full zippered, quilt-style sleeping bag that doesn’t require a sleeping pad attachment system. Note: EE doesn’t list their specs with their product listings but on a support page.
  • An Enlightened Equipment Revelation 40 (12.35 ounces) which can also open up as a blanket, is lighter weight than the Flex 40 and comes with a pad attachment system, but lacks a draft collar around the neck. It has 6.8 ounces of 900 fill power down (based on the manufacturer’s temperature ratings and a 72″ x 54″ sizing equivalent to the KB Flex 40. )
While the Flex 40 has a nice sleeping pad attachment system, the other aspects of the quilt such as the draft collar and amount of insulation it contains are more important.
While the Flex 40 has a nice sleeping pad attachment system, the other aspects of the quilt such as the draft collar, the foot vent, and the amount of 900 fill power down insulation it contains are more important when comparing it to competitive products.


The Katabatic Gear Flex 40 is a very nice quilt-style sleeping bag that’s quite warm to sleep with on a sleeping pad or in a hammock, even if you never use its sleeping bag attachment system or open it up in blanket mode. The draft collar and amount of 900 fill power down in the Flex 40 make it very warm quilt to sleep in, one that many people could likely use below its 40-degree temperature rating.

But people’s metabolisms when sleeping vary widely, and in the absence of any standard way of measuring quilt temperature ratings, the most important factor determining quilt warmth is still the number of ounces of high power down fill it contains. If you’re comparing top quilts from multiple vendors, don’t be fooled into thinking that a lighter weight quilt is necessarily better or warmer than another based on its total weight alone. Start by comparing the down fill power and weight and then use other warmth or comfort features as tie-breakers. Whichever way you slice it, the Katabatic Gear Flex 40 quilt is a winner

Disclosure: Katabatic Gear provided the author with a Flex 40 for this review.

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  1. My Katabatic Alsek is my main quilt and superb. I would like to get the Flex 40 for summer trips. Nice review and thanks. Also Enlightened Equipment do list the amount of down The sizing and specs tab.

    • Guess if I was too stupid to find the specs on the a support page, others will have the same problem. Thanks for the correction. Updated the text and now all good. I seem to recall that these specs were easier to find on their website before they upgraded it, but then I visit a lot of web sites…

      Been following your trips this year. You’re getting out a lot. Couple of years before your daughter starts roaming with you?

  2. I own two Katabatic Quilts, one being a Flex 40, and have found the temp rating to be spot on or better than published. Over the years I have invested in multiple top of the line down sleeping bags and they have always fallen short of their ratings, in some cases as much as 15 degrees. The pad attachment system works great and provides the flexibility to easily adjust for various temp situations. My Katabatic quilts are the only ones I use for my sleep system not only because of their performance but the quality is exceptional as well.

  3. Dear Phil, you mentioned that EE doesn’t list the amount of fill in their site. I thought that was odd, as when I bought my quilt a couple of year back they were very specific. I just went to their site, and their clear charts spec the fill for each size and temperature rating under sizing and specs.

    A 72X54″ Covert in 40 degrees will vary in weight a bit based on fabric choices, but will be in the 14 oz range with 7.57 oz of 850 fill, 7.11 oz of 900 fill and 6.88 oz of 950 fill. See

    My quilt matched the specs I was given, so I trust them. In the order process you can always request overstuffing.

  4. It’s worth pointing out that, when buying a quilt for use ground pounding, it’s important that you get the right size, meaning a quilt that is not too long. When you get in the quilt, connect the snap behind your neck and lie down, there should be a slight tension on the quilt that will cause the sides to hug your body. Simply tuck in and you should be draft free. I’m a back sleeper and can do without a pad attachment system. If your on the cusp size wise (like me at six feet) step down in length rather that up, which you would normally do for a sleeping bag.

  5. I purchased the Flex 22 for my 7-day JMT section hike this late summer (Labor Day weekend start). I’m a female side sleeper. The attachment system worked great with my Thermarest NeoAir mattress, keeping me draft free despite my tossing and turning side to side all night. The last night we had snow and freezing overnight, and I stayed nice and warm. It didn’t get warm enough on our trip to use the quilt fully blanket-style, but I look forward to using that option on future trips.

    I considered the Feathered Friends Flicker bag, and ordered both, but ultimately I didn’t see the point of a bag that zips up all the way when you’re a quilt user. The whole reason to go with a quilt is that the down on the bottom side of a sleeping bag (zipped all the way up) gets compressed and doesn’t provide insulation.

    • Both the FF Flicker and Katabatics quilts have continuous baffles. In other words you can move the down to where you need it if staying warm is a problem. In defense of the flicker, it works with *all* pads without the need to mess around with an attachment system, there are never any unwanted drafts, the zippers are taped so there’s never a fabric ripping snag, and there’s a down draft tube behind the zipper, something even the Flex could use. You can even use the flicker as an underquilt because it has suspension loops sewn into it. The Flex is nice, but I still like my Flicker 40 a whole lot better. :-) Katabatic Gear’s products are premium. But Feathered Friends is in a class all it’s own.

  6. I have a flex 22 and I have been very happy with it. I rarely use the attachment system because it tends to drape around me just fine.since I am not a small person, I got a wide model and I can simply connect the clips making it pretty much like a bag. I really like being able to use it pike a throw and I love that there are so many ways to regulate warmth by venting. I have been considering getting a 40 for summer use and I have compiled ed my 22 with a marmot back to get down below zero at right around 2.5 lbs total

  7. As one just getting into quilts, I found a sweet spot with the The Hammock Gear Burrow Econ. The company is unbelievably nice. Mucho bang for the buck!

    • Joe, I was looking at the Hammock Gear Econ quilt for my daughter as you can’t beat that price? Currently, I have an Enlightened Equipment Revelation 20 and like it but might even pick up an Econ 15 for myself for the price. How does it stack up comparing it to these quilts?

  8. I have had a Katabatic quilt for several years. I have found the temperature rating to be spot on. I actually use it consideerably below the rating and stay warm. However, I sleep very warm.

    I think an attachment system is critical. If your sleep system doesn’t require it, you don’t have to use it. But, most people will use it and if it wasn’t there, the wuilt would not be nearly as useful. THe Katabatic system weighs very little but works very well.

    Regarding the attachement system, inwarmer weather I only attache one side of the quilt. This allows me to open the other side while it is warm and then pull it over me as it cools down during the night. If the temperature gets near the temperature limit, I attache both sides to prevent draft.

  9. I just got the Flex 30 and tried it out for 3 nights on the Olympic Coast. It worked great and the temp regulation options are fantastic.

    These are now available in 850 duck down for a decent cost saving. I had heard that duck is more prone to odor, but even in the dampness of the PNW coast I had no issues.

  10. I know, I know, gonna ask another stupid question but does the attachment system work on a “classic” Thermarest pad 26×76? I have tried other pads but they were all too small for me since I roll around (and off0 them.

  11. Hey Eddie. I use an Exped Synmat UL7 – 25.5×77 rectangular – and the attachments system works fine with it.

  12. Hi Phillip,

    Just pulled the trigger on the Flex 30.

    Could you offer any additional insight on how to use continuous baffles to keep you warmer or cooler? Any pro tips to help expand the range of a bag up and down.

    Thanks for all the great info you put out. It’s really helpful and I always consult your site before any major purchase!

    • They offer marginal value on a quilt since it doesn’t have a back like a sleeping bag, but they let you reposition the insulation by shaking it where you need it most (or least). For example, if you have cold feet, shake the down to the footbox.

  13. Own both the Katabatic Flex 40 and Flex 22—each 900 fill. They are just fantastic, and fit all my needs. Mostly it is warm enough with the Flex 40, but with the Flex 22 you cannot go wrong.

    I am 6 foot 3 / 193cm / 95kg, so here are my 5 cents, my history of sleeping bags compared:

    old Finmark/ Ajungilak officially 3 Celsius Comfort—too narrow, in reality Comfort more like 10-12 Celsius: SOLD NOW
    extra wide Yeti Sunrise Comfort 800 XL, egg form XL, roomy but with 1400g much too heavy for UL trekking, comfort max 3 Celsius (even if specs said – 2)…..SOLD NOW
    Yeti was extra wide and heavy, but I still find my quilts more comfortable
    Zpacks 5 Full Zip in Long Wide: very warm, like -5 Celsius, but due too Mummy Cut I found it too narrow and mostly too warm. I also felt this needs care, I found here and there a few single down visible.
    So I bought in addition a Katabatic Flex 40 6’6″/W 900 for summer—perfect fit, roomy for my size, and surprisingly warm enough down to 5-6 Celsius —love it. Even if loft is not too high, I was surprised that it kept me quite warm – close to official rating.

    So since the Flex 40 F felt much better than my ZPacks 5 F Full Zip, I SOLD also my ZPacks 5 Full Zip for an additional Katabatic Flex 22 6’6″/W 900. I would take this for the EU Alps, the PCT or AT since I trust now that it will be good down to freezing, maybe a bit below with clothes. Alternatively I wanted to try the Enlightened Equipment Revelation 10, but I considered “never change a winning team.” Besides the form, I really like the material touch quality and the collar on top & bottom. Katabatic also comes with 2 attch systems but I prefer their unique cord/ clip in the loose position -since this is easy.

    Both have same cut 6’6 Wide, but 22 Flex has slightly longer footbox. Very interesting: My Flex 22 Footboxspans 7 baffles, my Flex 40 spans 6 baffles and the website shows span of 5 baffles…. not a major issue but somewhat strange.

    Otherwise I am a big Zpacks fan, but Katabatic was spot on for my needs, quality and touch are a bit more convincing than Zpacks. I bought the 900 fill, but 850 should be good enough too.

    • Hey there, are you from CT? I am as well. I appreciated your experience with the Flex quilts. I’m 6’3 as well and am torn between UGQ Bandit and this quilt. UGQ recommends an 84 inch length and 60 inch width for my size and being a restless ground sleeper. The Flex tops out at 78 inches and 58 inches wide. Do you find it plenty long and wide enough being sane height? I’m also 215-220 lbs, 54-55 shoulder girth. Is there enough room to pull up over head a bit if need be?

  14. Do you know if the flex 40 is ever coming back? I’ve been trying to reach Katabatic Gear for a month & there’s been no response…

  15. I have the flex 30 and couldn’t be happier with it. It is my first quilt, I have had it for a few years. I do most of my hiking on the AT. I live in the northeast. I got the regular wide, I am 5’8 180 pounds, I probably could have gotten away with the regular-regular but the reg-wide has a little more down in it and when temps drop below the limit and I have all or some of my clothes on thermals, mid layer and down coat it is nice to have a little extra room. I always use a thin liner to keep it clean and a little extra warmth. I can also shake the sides and put down over me. When I snap the back I don’t even have to use the straps.,the way it is cut is perfect for me. I have had it down below the limit a few times. I have no other quilts to compare it to but I have never regretted buying it. It is very versatile. The only nick I could give it is I am always afraid that the zipper underneath your legs, just hangs there,I am afraid that it will pop my x-lite. I always lay my t shirt on top of pad under the zipper.

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