Home / Gear Reviews / Tents, Hammocks, and Tarps / Winter Bivy Selection

Winter Bivy Selection

Integral Designs Overbag Bivy in eVent Fabric

I've been agonizing over the selection of a lightweight winter bivy bag for a couple of weeks and I thought I'd come to a final decision when I ordered the Integral Designs Overbag Bivy. This bag is completely made using eVent fabric and is considered to be one of the most breathable bivies available. But, it doesn't have a zipper! I realized this a little late in the game.

But let's start at the beginning….

This year, I decided to switch from a tent to a floorless pyramid tarp for winter camping, augmented with a bivy sack for moisture management and extra warmth. I've gotten really used to sleeping in a bivy this year under all kinds of different tarps and I've really come to like them.

After sifting through the various winter bivy bags available, I narrowed my decision to the Integral Designs Overbag ($240) or an Alpine Bivy from Mountain Laurel Designs ($290 – extra long with a side zipper). The Overbag is made using eVent while the MLD Alpine Bivy has an eVent top and a silnylon floor. Upon request, MLD will also sew a custom, all-eVent version of the Alpine Bivy, for a hefty premium.

Ultimately, I decided to go with Integral Designs Overbag despite the fact that it is heavier than the Alpine Bivy (18.7 oz vs 13.75 oz) in the configuration and long sizing I wanted.  In the past, I've experienced some condensation where a sleeping bag touches a bivy made with silnylon, something that would be avoided using the Overbag.

Integral Designs Overbag

Mummy Hood with side compression loops. Top hang loop is my modification threaded through eVent Label

To confirm my reasoning, I posted a thread in the Gear Forum at Backpackinglight.com. I came away after an informative discussion with the understanding that an all-eVent bivy was likely to perform better in snow shelters because eVent has a higher hydrostatic head than silnylon, so I went ahead an ordered the Integral Designs Overbag from Amazon, where it is heavily discounted to about $170.

A week later I received a package from Amazon containing an Integral Designs Sil Tarp 2, and not an Overbag. I was not happy. Moreover, when I tried to return it, Amazon couldn't get past the fact that the product they'd sent me didn't have an ISBN. I eventually managed to get a full refund, but that's the last time I'm going to order a bivy bag from Amazon.

I found another retailer, Backcountrygear.com, that carries the Overbag and ordered it, paying full price. The OverBag arrived after a week and I tried it on in my living room with an Exped Downmat and a Western Mountaineering Puma -25 (F) sleeping bag. Man, is it big! It swallowed the Puma and the Downmat without causing any loft compression in the sleeping bag. So far, so good.

I inspected the stitching around the bag, which is nicely taped, and checked out the eVent fabric. But as I lay there on the floor, I realized that the Overbag bivy was going to be hard to get into and out of at night, in the dark, under a tarp, in the dead of winter. Let's just say that I drink a lot of fluid in the evening when I go winter backpacking to rehydrate and prehydrate, and I can't hold it for 12 hours at night.

Integral Designs Overbag Bivy

OverBag: Two side cord locks on either side of a peaked mummy hood

Without a side zipper, the only way to get out of an Overbag is to do something that looks very much like a wet exit from a kayak.
If you have no idea what I'm talking about – the motion is similar to taking your pants off while sitting down. I just can't see doing this in a snow shelter and staying dry. The same issue arises with getting your sleeping bag into it all the way: you need to be wearing the sleeping bag first, and then slide into the bivy.

Hence the need for a zipper.

I admit it. I have been completely spoiled by the zipper on my 3 season MLD Superlight bivy sack. So, I'm returning the Integral Designs Overbag and I've bought the MLD Alpine Bvy instead, in a size long, with the zipper option. On hindsight, I can live with a little condensation if it happens (and it might not in dry cold), given that my winter trips are at most 2 nights long. Having a zipper is probably not ideal on a winter bivy bag, but I will also be levitating on a 2.5 inch inflatable down pad, so even if snowmelt does enter the bivy sack, it will pool well underneath me.

Integral Designs sOverbag Bivy - Size

Size comparison with 32 oz Hunnersdorf Water Bottle

Lessons Learned

I'm always looking to understand the lesson behind my experiences, and I guess the lesson here is that their no use resisting the CRACK that Ron Bell sells at Mountain Laurel Designs! He should set up an automatic payroll deduction plan for his customers so we can dispense with paying him.

No seriously.  It was good that good that I tried using the Imtegral Designs Overbag at home in my livingroom and envisioned using it before taking it on a trip and nullifying the 60 day return policy. I obviously overlooked the need for a zipper until I was forced to get into and out of the OverBag without one.

Most Popular Searches

  • Winter bivy
  • winter bivy sack
  • best winter bivy


  1. i picked up a new ID Microbivy for 135$ … ill crawl into my bag for that price … lol

  2. Urgh, yes, that won't do. Bivvies are challenging enough in winter, even *with* decent zippers. Shame about the ID Overbag, though – I've been using the ID Penguin Reflection bag for the past winter, and have been very happy with it.

    I suffer the same effects as you after re-hydrating on those long winter nights. But there's no way I'm getting out of my bag. I think the pee bottle may be one of mankind's best inventions…

  3. I remember you saying that you got one. Does the reflective coating significantly add to the heat retention?

  4. My solution to the no zip dilemma was to have one fitted, it increased the weight, but it is easy to get in and out of, and as you noted is very roomy and is an ideal cool/cold weather bivy.

  5. "no use resisting the CRACK that Ron Bell sells at Mountain Laurel Designs"-

    That would be hilarious if it was't true!

  6. When exiting my ptarmigan I felt more like a butterfly exiting its cocoon, getting back in…well even butterflies with a pinhead-sized brain don't try that. Enter that MLD crack dealer.

  7. Yes, you were right to switch to a zipped bivy. That crazy no-zip bivy dance/wiggle is a pain in the a**. My XL MLD Side Zip Soul bivy is more than big enough for an Exped Synmat and a winter bag/quilt combo too.

    Talking of pee bottles, those of us using Real Turmat dehydtaed meals are carrying a pretty efficient pee bottle without realising it. The empty packet with it's sealable top makes a great dual-use, no-extra-weight night time bathroom substitute…

  8. Good idea to reuse the food bag. I'm paranoid though. I like a wide mouth Vitamin water bottle for such things.

  9. Honestly, I don't think the reflective coating on the Penguin bivy does much. Having said that, the material breathes much better than eVent, so that's a big check in its favour.

  10. Great post, Philip.

    I used a tyvek bivy with sidezipper last winter, 205 g, beats eVent by miles in breathability, but not in waterproofness. As I camp on snow and have my CCF pad usually outside the bivy that ain't a big deal, though.

    Am happy with my custom MLD Alpine with Dyneema bottom, no side zipper, though. But I am still young and flexible and empty the blatter three times before laying down to sleep, so I can cope with it :D

  11. My 3-season bivy is a Ptarmigan from Titanium Goat. I totally agree about the side zip, so I asked DJ to add one. No problem, $20 extra, even though he "doesn't see the need". He must be a lot more flexible than I am.

    It is a short zipper, but really helps.

    I've had condensation in the foot of my bivy a few times, mostly when I was sleeping without a tarp. I think your feet just don't make enough heat to cook the moisture out. I check when I get up, so I air out the bivy and the bag a bit before packing.

    I back off on hydration a couple of hours before bedtime to reduce the pee bottle usage. It helps some. I favor a robust vessel for the pee bottle. I'd rather not roll over on top of a ziplock bag full of pee.

  12. I was looking at an MLD bivy for my PCT thru-hike, but it came down to money. I just couldn't spend what I wanted!

    So I went with a lightly used BPL Vapr bivy, with a professionally added side zip. Found it on BPL for $109, which included shipping from Australia. :) I couldn't pass it up. It's made with eVent, so I was pretty excited; not too much of a fan of some other materials for breathability. This will be my first foray into bivy-livin', and I'm teaming it up with a Alpinlite Gear 'Terraform III' tarp.


  13. The Titanium Goat Ptarmigan bivy is a great deal at $90. Mine was more, because I added the net window ($25) and the "ask DJ if you want one" three-foot side zip ($20).

    The Ptarmigan has a tight-weave nylon top with DWR, so it is very breathable. It isn't super roomy, was too tight with my 20º Western Mountaineering bag plus a Therm-a-rest, so I keep the pad outside. Also, a pad makes the bivy straight, so the bivy won't move when I pull my knees up.

    Ti Goat has a Raven XL bivy that is bigger.


Leave a Reply

Your email address will not be published. Required fields are marked *

Subscribe To Our Newsletter

Join our mailing list to receive our weekly newsletter. No spam. Just honest gear reviews and backpacking articles. 

You have Successfully Subscribed!