Sea to Summit Ultra-Sil Backpack Liner Review

Lately, I’ve been writing longer more in depth reviews. While I think that may be a good approach for some, generally speaking I think most folks don’t read the entire post, and are mostly looking for the quick and dirty details. So, for the next few reviews, I’ll be trying out a shorter, more condensed format.

Sea to Summit Ultra-Sil Backpack Liner


If you don’t use a pack liner, you should. Dedicated pack liners are more user friendly, more durable, and more environmentally sustainable. In my own research, the Sea to Summit Ultra-Sil liner is the best so far that I’ve found on the market. Ditch your trash bag and shell out the $40 and get yourself a pack liner, you won’t regret it.

Sea to Summit Ultra-Sil Pack Liner still allows for easy access to backpack (shown here in HMG Southwest 4400)

Test Conditions

This pack liner was put to the test during a summer of instructing for the Colorado Outward Bound School. Since its purchase in April of 2017, this pack liner has been used for over 80 days in the Colorado Rockies. I used this bag as my sole waterproof mechanism for all of my things (sleeping bag included) which were all stuffed into this one bag with no separate waterproofing of any kind. I purchased this product with my own money, and am not affiliated with Sea to Summit in any way.

Sea to Summit Ultra-Sil Pack Liner rolled up inside HMG Southwest 4400 pack.

Sea to Summit Ultra-Sil Pack Liner rolled up inside HMG Southwest 4400 pack.

Performance & Usability

The Ultra-Sil liner comes in three sizes, and is essentially a giant, thin dry bag to line your pack. It seals shut at the top like any other dry bag. I prefer to organize my equipment, and pull the liner out each night to keep my stuff dry and safe, and flatten my pack and leave it under my feet. Sea to Summit recommends leaving the back inside the pack in order to maximize durability. Well, after 80 days of removing the bag and putting it on the ground of my bottomless mega-mid, its no worse for the wear. (Fabric is 30D Cordura) The bag itself isn’t the most waterproof stuff sack in the world. I’d venture that if you left it out in the rain or submerged that it would soak through after a few hours, but for it’s intended use, you shouldn’t have any issues. I had one course this summer with 14 out of 15 days of rain, and had no issues keeping everything dry. That being said, this is not recommended for your river rafting trip. Get a designated river bag for that.


  • Lightest 100% waterproof solution (3-4oz depending on the model) when compared to alternatives like rain cover + waterproof stuff sacks

  • Variable sizes (50L, 70L, 90L)

  • Cheep ($35 - $45) - nearly the same price as any waterproof stuff sack and certainly cheeper than the waterproof dry compression bag + raincover combination

  • Easy to use

  • Environmentally sustainable (will last for many years vs your trash bag which will not, at least for me anyways)


  • Concerned about overall durability - 30D fabric is easier to rip accidentally and will wear faster over time. Would prefer thicker fabric that was a few ounces heavier overall

  • Additionally concerned with the need to rely on sewn velcro to assist with closing/storage of bag. Over time more likely to wear vs buttons. (Velcro does not affect waterproofing/seal)

  • Doesn’t keep the outside of your bag dry. (I’ve never been a fan of a raincover, particularly in the stormy, windy Colorado alpine, and don’t like using waterproof compression bags for my sleeping bag because they are bulky, heavy and affect the ability to efficiently pack the pack overall.)

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