This compression sack currently stores my winter coat, hat and a pair of wool socks while I one bag travel internationally and without this compression sack I would be hard pressed to be prepared for winter conditions and still fit everything into one pack. These are a go to essential.I tore the original stuff sack for this sleeping bag and like the seatosummit brand for other dry bags. I ordered the xl and it fits my sleeping bag perfect and it ends up taking less space than before because you can compress it more in this stronger bag.I got the XL Compression Bag. Very durable and Quite compact, but it fits my Nemo XL/Xtra wide sleeping bag single. I will be buying more for other storage! Thank you for a great product!I was looking for a waterproof compression sack for my sleeping bag for backpacking trips (thinking more heavy rain than it falling in a river). The one thing I really like about this bag is it functions just how you would expect a compression sack to function, which is saying a lot considering it is also a dry bag. In particular, I was impressed that it will allow air to escape even when sealed. I liked it so much, I even got a second one for my clothes.I only have two suggestions:1. Other compression bags have buckles on 2 of the straps (rather than just straps). This makes it a little easier to get the lid off quickly. That feature would make this perfect. -- See pict2. I like this as a solution to make sure my backpack items stay dry (this task was previously relegated to ziplock bags). It would be nice if they came in different colors so I could tell the bundles apart. (e.g. blue socks, red shirts, etc...)S2S is a great product. ?Saw tons of Youtube videos saying this product was a great option for a dry bag and compression sack in one and it sure works well! I have a Kelty Cosmic Down 40 and I thought it was small *before* compression. I ordered the Small and the sleeping bag went from 14'x8' to 8"x6.5". The only downside is that because it is so small and lightweight, it likely cant take a beating, but by no means is it low quality, that's just a consequence of being so compact that *any* other brand would suffer from as well.A great buy, you can't go wrongIt works for keep bad water away from sleep bagI purchased mine back in 2014. It didn't stay waterproof very long. Works better as a compression sack, not as a drybag.Wasn't sure at first, because it seems to quite flimsy on first inspection. However now it has been used it seems to in fact robust and well made. Only time will tell I guess. It seems to be well waterproof, but I have not tested thoroughly enough for this to be guaranteed. Certainly it is water repellent. Again time will tell. :)As it is not listed elsewhere, that I saw the sizes are as follows:XL : 27 cm x 58 cm; 210g; 30 litre max; 10 litre min.L : 23 cm x 50 cm; 168g; 20 litre max; 6.7 litre min.M : 20 cm x 46 cm; 148g; 14 litre max; 4.5 litre min.S :18 cm x 40 cm; 129g; 10 litre max; 3.3 litre min.XS : 15 cm x 35 cm; 107g; 6 litre max; 2 litre min.These are their figures, not mine. :)It began its travels with me cycling down England, in Janury 2013, on the back of my bike. Then withstood 2 months in Morocco. Since then it has been away on 100+ camping trips, in countless amounts of rain and mud.Pros: - I use it to hold my down sleeping bag and maybe the odd piece of clothing, for which the size medium is ample. - You can pull the straps tight to compress it, which can be better or worse depending how much is inside. - Fully watertight if you seal it properly. - Repairs can be made with GAFFA tapeCons: - When I first bought it I tried to squeeze my sleeping bag in in its case, but that ripped the side a little (see photos). I repaired with some GAFFA tape and it's still going strong. (This was my own fault anyway for trying to put my sleeping bag in in its other case. Best way is just to STUFF clothing or sleeping bags inside.)I don't do many reviews, but this piece of equipment has just been so useful I had to. I've got more than my moneys worth for it :)FYI in the photos I had two jumpers and a big towel inside.I bought the compression bag for my sleeping bag as I go kayaking and always tight for space in the hatches for all my gear. Sleeping bag is crutucal gear so to mitigate the risks of water damage I wrap my sleeping bag in two light weight dry bags.The first photo (red bag) is the sleeping bag with sea to summit compression bag plus one lightweight waterproof bag over the top. The second photo (yellow bag) is with the sleeping bag in a normal cloth compression bag followed by two light weight waterproof bags. I have put another sleeping bag beside it for comparison.As you can see Using the sea to summit compression bag rather than the normal cloth compression bag I haven’t made the overall bundle much smaller . Whilst the sea to summit bag made a minor difference it’s unremarkable.Disappointed at the volume reduction.Wondering if the photos that sea to summit use to show volume reduction are showing stuff in the bags that compresses down far more easily than my sleeping bag, which isn’t made of down but synthetic materials.Anyhow I feel For my use this sea to summit bag has not made enough of a difference to justify buying this one when I have other bags that get do almost the same result.The bag itself is otherwise of good quality though I’ve not tested actual waterproof nessExcellent compression sacks. The large is has enough room to get my Hilleberg Soulo tent in [minus the poles], my Marmot Hydrogen down bag & a NeoAir Trekker. It compresses all 3 down to a third of their size & the waterproof test? While I was playing with it to see what I could get in there, we had a Mountain Rescue shout & I raced off, leaving the compression sack in the back garden with my down sleeping bag inside. The nice sunny day that it was, turned into a monsoon in the late afternoon & on return 6 hours later I realized what I had done, brought it inside, pulled the sleeping bag out - bone dry! It's the best endorsement I can give at the moment, but spending a little more on quality equipment is the best way to spend less, replacing quality equipment, subjected to failure because of poor quality equipment.25 years climbing the planet & working with MRT.These really do squash stuff to a third or quarter of the original size. Kneeling on one of these provides a better result even than vacuum bags with a powered sucker. The ‘hat’ is essential, since it prevents expansion even when air can get in, which is more difficult to stop than you may think. These are strong, well-made and do what they say they will. I’ll probably buy more for my camping gear.Shown on photos are the XL (double sleeping bag inside), L (2 x memory foam pillows, towel) and M (large inflating cooler bag).