Sleeping Bag Liner, 3F UL GEAR Tyvek Sleeping Bag Cover Liner Waterproof Bivy Bag Camping Bags Ventilate Moisture-Proof Warming Every Dirty Inner Liner BIVY Sack (B Type)

This product is so light weight and completely comfortable. My favorite hiking gear item along with my Trekology sleep pad. It is very quality item and worth it. I always have this camping with me and plan to try it out with just a sea to summit sleeping bag liner in the summer. Whoever sewed this together, whoever made this, thank you! I love this with all of my heart.

I used this as an external bivy around my 40 degree down bag. I was hiking in the White Mountains, and the temperatures can quickly drop and the weather can change every 15 minutes. I used this inside my tent as a way to keep condensation from the rain off my bag and it worked wonderfully. I was cozy all night, and even had to open up the top a bit to vent some heat at one point. Very pleased with this purchase.

It seems there are two different models sold here: "Type A" and "Type B". Type A appears to have an open back and no zipper, such that you just tuck it around a sleeping bag. Type B has the opening on the top, with a zipper, and draw-cord inside a bit of red nylon around the face opening. My purchase & review are for "Type B" only.For context, I'm into alpine climbing, and am often willing to sacrifice comfort in order to have the lightest possible gear. I have spent a lot of nights outdoors sleeping in various other models of bivy bags, ranging from quite-expensive to one of my own attempts to home-make my own bivy bag out of tyvek. I'm reviewing this one immediately after unboxing it, so I haven't slept in it outside yet, but given my experience with other bivies, here's how I think this one compares.I think this one is close to ideal, but not quite. My only complaint with it is the width. I've measured it as 34" wide at the shoulders, and I wish it was more like 36" or 37" wide there. (But no more, because the biggest selling point of this is how light-weight it is.) I'm 5'8", and weigh 175lbs. If I put an inflated thermarest inside of it and get in there with it, it's just barely the right amount of space for me. There's just barely enough room for a sleeping bag to loft a few inches around me. It wouldn't take much movement though before I'm pushing an elbow against the tension of the tyvek due to moving an arm or rolling over. If you're my size or smaller, this is okay, I could definitely spend a night sleeping in this, it's just got no margin for being any larger than me. You could create more space by putting your pad outside your bivy, but for me personally the pad must be inside because (1) I prefer quilts (like Katabatic or Enlightened Equipment) which must attach to the pad, and (2) I want a bivy to act somewhat as footprint guarding my inflated thermarest from direct contact from the ground, which is sometimes a rocky bivy site, and I'm certainly not going to carry a second & separate ground cloth when I'm trying to cut every ounce I can. So for me the pad has to go inside, and that makes things almost-tight with the bivy being 34" wide at the shoulders.If you are my size or smaller, for the price ($49,) I do think this bivy is a great deal. IMHO, the purpose of a bivy bag should be as light as possible (if a bivy bag weighs a pound or more, then don't bother, just bring an ultralight tent instead.) By that measure, this bivy does a superb job, weighing in at a hair over 7 ounces. I've had trouble finding other bivies in this weight-range, with the closest competitor being the "Katabatic Bristlecone Bivy", but that costs almost three times the price, and likely has a less water-resistant material. And to be so light-weight, you shouldn't really be expecting "perfect" weather-protection from it anyway; no sufficiently lightweight bivy is meant to keep you perfectly dry during a heavy rain. Instead, the purpose of a lightweight bivy is to help you fend off a light sprinkle, or stop the wind, in case you went on an overnight climb when the weather was supposed to be good, but was slightly worse than expected. I think the construction of this bag is likely to do so admirably. Based on the feel of the fabric, I'm guessing this is made out of Tyvek 1443R, which is lighter & softer than the more ubiquitous Tyvek Home Wrap. This bivy should turn out to be reasonably water repellent enough. In this bivy's construction, the seams are not taped, so there are tiny pin-prick holes along edges, but I'm not that worried about them, I still think this would be fine at keeping the majority of water off of your sleeping bag during a light sprinkle. I'm impressed a the double-stitching along the zipper to add reinforcement there. I'm also glad to see that the zipper has pull-tabs on both outside and inside, which is rather important for getting to close yourself up once you're already inside. And the elastic draw cord around the red-nylon face opening is a nice touch too. It's pretty well made for a cheap bivy. In addition to planned overnights, this could also be useful to carry as an emergency bivy for any sort of first-aid situation, say on ski tours, in case you want something a little more durable than those shiny mylar emergency bivy-bags.Some specs according to my own rough measurements:- weighs 7.2oz on my kitchen scale, and that's the combination of bivy + stuff sack together- width at shoulders: 34" wide, while laid flat- width where my feet would end up: 25" wide, while laid flat- length: 82" end to end (or 72" from bottom end to the horizontal opening at the top of the zipper)- while packed inside it's stuff sack, it's about the same height as a nalgene. Uncompressed it looks about the same width as a 1L nalgene bottle, but in reality, it's notably skinnier once anything is pressing on it.- my last picture shows it next to a Therarest "Womens NeoAir XLite" pad, for comparison, which 66"x20"

Type (B). It is exactly as described. Add some seam seal tape and it will be great for skinny people with narrow shoulders and small chest if 6’ or shorter with room for a sleeping bag (no room to include a inflatable sleeping pad). If the zipper is left open, it will likely work for a 6’ tall average sized man with sleeping bag to keep their sleeping bag dry from condensation inside a single wall tent. If they would add 6” in length and 8-12” width with sealed seems, this would easily be a great lightweight stand alone bivy.

Nearly a perfect ultralight and affordable option for use under a tarp. Unfortunately it is too tight around the hips / chest area when zipped and compresses your down rendering it less effective. Especially bad when turning sideways. An additional ~8-10" circumference would alleviate the issue and I'd give it 5 stars.I am using a Thermarest X-therm and an Enlightened Equipment down quilt.

This is great, if it's not raining. The zipper isn't sealed, water will absolutely get inside. If they'd seal it I'd absolutely buy it again, I'd even pay more. Tyvek is pointless as a liner if it's not sealed.

To start I'll get the bad out of the way. The difference between "Type A" and "Type B" was a little confusing. Fortunately I was able to figure out which one I needed based on comments left by other people. To be clear, I got the "Type B" which was the one with the drawstring mummy-style hood and the zipper. I highly recommend paying the extra few bucks to get that over the Type A version.Then there's the good. To start, the price was right. Most bivy bags cost far more than this even for the lower quality ones. Tyvek is sturdy material and doesn't rip easily (unfortunately my dog did still tear a hole in it but that was easily fixed by purchasing some Tyvek tape). The bivy is incredibly spacious. I'm not a big guy but I've used other brands that felt much more confining and were more difficult to get in and out of. I used it while camping in my hammock and it did a great job of cutting the wind. It didn't rain so I can't say how well it will hold up. I did test it in my shower. The material got damp on the inside but not really wet and there was no water pooling inside, so I suspect that it would perform similarly in the rain.All in all, this was a good purchase.

I use this bag for warm weather layering, when the weather is bad. Well made for an inexpensive bag. Material is tough and durable.Tyvek is great stuff for this purpose, just be careful to regulate your insulation so that you don't sweat inside it. Tyvek is breathable...but not overly so.

3 nights in single wall tent with this over a down bag. Probably added 5 degrees warmth. Minimal condensation inside bivy sack, less than i thought. After the third night toe box of my sleeping bag was damp, (my tent dripping on me) the bivy sack maybe leaking slightly but tough to tell....it held out long enough and happy with purchase. Very light.

Not the weight advertised. The seems are also not taped, rhey are stitched woth very obvious holes. It is large though. Returned.