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Sea to Summit Ultra-Sil Compression Sack

rated 4.0 of 5 stars
photo: Sea to Summit Ultra-Sil Compression Sack compression sack

Good for keeping one of my most important pieces of gear dry—my sleeping bag. It's ultra lightweight and fairly waterproof. Compresses nicely with strong tabs.


  • Lightweight
  • Packs easily because of the slippery material
  • Waterproof


  • Price—a bit expensive at $32.95 USD
  • Durability of the lightweight material

I bought this lightweight compression sack in a size medium, which is perfect for my Marmot Never Summer 0 degree bag, which weighs in at 3 lb-4oz in a size long. I listed this information because when I bought the compression sack I was guessing at what size would be the right fit for my sleeping bag.  This bag compresses down nicely in a size medium stuff sack. 

On the other hand I used it for my summer bag which is a North Face and weighs about 1 -1/2 lbs.  The size medium is much too large for this size of a bag. So anyhow, you can use that to figure out which size might suit your bag the best. I would get a size small for the 1-1/2 lb down bag.

The reason I bought this item is because keeping my sleeping bag dry is really important to me. I can trudge uphill all day long and don't mind suffering, but I want a nice dry bag that night. The compression straps work well and the doubled over tabs at the ends keep them from slipping through the buckles. You can really pack a bag down to size with the four compression straps.

All of the sewn on items seem to be sewn well and the construction seems pretty solid. The material that the bag is made of though is super lightweight though. Once we reached camp I used the compression sack to hold a six pack of beer that I hauled up and dunked them in the lake to keep cool. As I expected, the bag was waterproof and would not sink right away with the 6 beers in it. That convinced me that the sack was waterproof enough for my purposes, which is to keep my bag dry in a drizzle or during a river crossing. It took quite some time for the bag to eventually sink with the beers in them. I know this wasn't the designed purpose, however I thought it was a good test of the waterproofing. 

When I pulled the beers out a few hours later I noticed that the sack had two small holes rubbed in them. The sack was placed in a very calm location and you wouldn't expect any holes to be rubbed through the material while sitting in the water for a few hours, but that's what happened.

So my final thoughts are that the bag is pretty decently made with waterproof and lightweight materials. I think that the material may be a bit too thin though and its durability may come into question. Also, at $33 USD the price is a bit high.

Had it not been for the holes rubbing through the bag in just a matter of a few hours I would have rated the bag a 4 or 5. With consumers and manufacturers focusing heavily on weight savings in their materials and design I think that many of the items we use now don't hold up like they did when they were just a bit heavier. Just my opinion (I realize this is coming from a guy who will pack a 6 pack into the high country, so weight is a concern, but not my primary concern).

Source: bought it new
Price Paid: $32.95

The small version of this sack allows my daughter to carry both her sleeping bag and pillow in the bottom zipper compartment of her TNF Terra 45 pack. Durable, slippery material squeezes right in.


  • Durable rip stop style codura ultra-sil material
  • Lightweight
  • Slippery material makes putting in/pulling out of pack easier


  • None

Basically, the pictures tell the story:

Here's the Kelty Cosmic Down 20 degree bag in its storage sack.


Here it is in the Sea-to-Summit uncompressed (compared to a Nalgene bottle).


And in its final compressed state.


One of my twins is fairly slight in stature (98 lbs) so her pack is The North Face Terra 45.  When her sleeping bag was stuffed in the sack it came with, it took up the complete zippered compartment in the bottom of her pack. Since she was already limited in space, we decided to try this S2S Ultra-Sil Compression Sack.

(Note: I have a couple of Granite Gear compression sacks I've used over the years but they are made of a heavier weight material and I'm thinking of getting the medium version of this sack for my sleeping bag. The weight difference between the Ultra-Sil and the regular Granite Gear material is quite noticeable.)

I'm interested to see how the material and the seams hold up over time since it is more delicate. The material has a rip-stop type of weave so even if it gets a hole in it I think it will resist getting larger.

Source: bought it used
Price Paid: $15.50 on ebay

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Price Current Retail: $32.95-$52.99
Historic Range: $0.77-$52.99
Reviewers Paid: $15.50-$32.95
Product Details from Sea to Summit »

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