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Sea to Summit Ultra-Sil Dry Sacks (Production) SPOTLITE REVIEW

The lightest dry sacks, but also the leakiest (compared to lightweight dry sacks from four other companies) when subjected to harsh conditions.


by Carol Crooker | 2006-06-28 03:00:00-06

Sea to Summit Ultra-Sil Dry Sacks (Production) SPOTLITE REVIEW


Sea to Summit Ultra-Sil dry sacks are incredibly light. And, like other ultralight gear, the user needs to know the limitations and use accordingly or be disappointed in the performance.

I released a SpotLite Review of prototype versions of these dry sacks in August 2005. I have now tested two production dry sacks and compared their performance to dry sacks from Outdoor Research, Cascade Designs (SealLine), Granite Gear and Pacific Outdoor Equipment. The Ultra-Sil dry sacks did not fare well in these tests.

Although the web site does not indicate anything other than that the Ultra-Sil dry sacks are waterproof, the instructions that come with the sacks say, “Ideal for keeping contents dry in any situation that the bag is not submerged.” Also, as noted in the 2005 SpotLite Review, the Ultra-Sil Dry Sacks are waterproof when used as designed, according to the US marketing rep. She adds, "If you are going to be getting really wet, as in floating them in a river, we also recommend another layer of protection for expensive items such as cameras or GPS. They are not recommended for prolonged submersion."

Other lightweight dry sack manufacturers include similar caveats and all the dry sacks tested provide more protection from moisture than a typical stuff sack.

However, even the caveated claims did not hold water in my testing. The Ultra-Sil bag did not keep its contents dry after 10 minutes under a hard shower with seam side up. The Ultra-Sil bag did successfully safeguard contents when standing upright under a shower for 10 minutes. Of course, a dry sack inside a pack is unlikely to experience such conditions.

It was disappointing that these dry sacks - the lightest by a significant amount of all the dry sacks commercially available - also did not satisfy the following claim, the “Dry Sacks will not leak in that situation [dry sack in the bottom of the pack … partially submerged underwater for quite some time]." The prototype dry sacks did not pass this test, but Sea to Summit was sure that further tweaking of the taping technology would stop water leakage through the seams.

However, the round bottomed Sea to Summit dry sack performed the worst of the dry sacks I tested in two tests with the sack sitting upright and on its side (seam down) in a couple inches of water for 8 hours. The idea was to simulate a worst case scenario, e.g. backpacking in horrible storms in Patagonia resulting in a couple of inches of water in the bottom of the pack at the end of the day. Contents of the Sea to Summit dry sack were soaked after this test. Two other bags failed one or both of these tests, but allowed just a wet spot or two on bag contents.

The Ultra-Sil sack leaked so badly after 8 hours in shallow water that I wondered if some water might be soaking through the fabric. To check this idea out, I formed a small pocket in a sack where there were no seams. I put a t-shirt in the pocket, closed it off, and sat the pocket in water. The t-shirt was completely dry after 8 hours. The fabric is not leaking when immersed in shallow water - the circular seam is the main culprit.

Happily, Sea to Summit appears to have improved straight seam taping procedures since the prototype I tested. The production dry sack with a straight seam on the bottom kept contents dry after standing on end in water for 8 hours and during a 5 minute submersion test.

The Sea to Summit dry sack was the only one tested to leak through the roll top closure. It appears that the very things that make these sacks so light contribute to this. The Sea to Summit dry sacks use Siliconized Cordura fabric. It is very light, and did not absorb water during a 10 minute hard shower (see Lightweight Dry Sacks: Comparison Testing Results). Fabric on the other sacks I tested absorbed some water which kept at least some water that was working inside the roll top closure towards the top of the dry sacks from making it all the way. The Sea to Summit sack is the only sack that doesn’t use webbing along the top opening. Sea to Summit sacks have a lightweight ribbon/tape and plastic stiffener at the top opening. The webbing used on other sacks absorbs more water than the accoutrements at the top of the Sea to Summit sacks and helps to keep water out of the inside of the pack.

Keep in mind that much of my testing was harsher than a dry sack will normally experience inside a pack. The Sea to Summit dry sacks provide more water resistance than a normal stuff sack at not much more weight. The prototype Sea to Summit Ultra-Sil sacks I tested in the field and at home by floating them in a pool of water, kept my gear dry. The reason - both the round and flat sacks floated with the round seams out of the water.

Sea to Summit recommends double bagging valuables. Double bagging using a Gossamer Gear pack liner and Sea to Summit Ultra-Sil Pack Liner or dry sack is still quite light. I used a prototype 20 liter Sea to Summit Ultra-Sil dry sack (1.8 oz) and a medium Gossamer Gear Pack Liner (1.3 oz) inside the Gossamer Gear G6 for a SuperUltraLight canyoneering trip. I floated my pack on a TorsoLite self-inflating pad when I needed to swim, and the pack contents stayed dry. The total weight, 3.1 ounces, for double bagging using these options is still less than most 20 liter dry sacks.

Note that I have not done any testing on the Ultra-Sil dry sacks to determine how their performance holds up with use.

The Ultra-Sil dry sacks offer viable options for ultralighters who know their limits and manage them properly. For those who want more protection and are willing to carry the extra weight, Sea to Summit also offers Lightweight Dry Sacks constructed from 70-denier nylon, laminated with polyurethane with weights still in the lightweight range (e.g. 3.7 oz for the 13 L size, same size Ultra-Sil weighs 1.4 oz). Other companies also offer heaveir, more robust options - see the listing in Lightweight Dry Sacks: Comparison Testing Results.

Features and Specifications

Dry Sack

  • Super compact and ultra lightweight
  • Made of Ultra-Sil nylon, a polyurethane coated Siliconized Cordura
  • Watertight, non-wicking Hypalon roll top closure with stiffener at the top for a better seal
  • Soft and flexible with a slippery finish for easy packing
  • Nearly transparent allowing good visibility of the contents
  • All seams are double stitched and tape sealed
  • Smaller sizes have flat bottoms, others are round
  • Uses low profile buckles

Pack Liner, additional features

  • Ultra-Sil Pack Liner opens wide for easy packing when it’s inside a pack
  • Unique top closure: extra fabric at the top folds in and velcros in place, then rolls down, creating a more compact closed loop at the top
  • Designed to fit the internal contours of a backpack, so the base is oval, rather than round
Weight Specified
Weight Specified
1 611 6 x 9 (flat) 15 x 230.7 208.95
2 1222 8 x 12 (flat) 20 x 300.8 2310.95
4 2444 9 x 15 (flat) 23 x 380.9 [0.8] 26 [23]11.95
8 4888 6.5 x 18 17 x 461.1 3015.95
13 79313 8.5 x 21 22 x 531.4 [1.4]40 [39]18.95
20 122020 10 x 24 25 x 611.8 5022.95
35 213635 12 x 2730 x 692.3 6529.95
Pack Liner Small30005021 (H) x 19 x 1653 x 48 x 412.67434.95
Pack Liner Medium43007035 x 20 x 889 x 51 x 203.49639.95
Pack Liner Large55009048 x 22 x 10122 x 56 x 254.412544.95


"Sea to Summit Ultra-Sil Dry Sacks (Production) SPOTLITE REVIEW," by Carol Crooker. (ISSN 1537-0364)., 2006-06-28 03:00:00-06.