Sea to Summit Ultra-Sil Pack Cover Review

Overview

The Ultra-Sil Pack Cover is a seamless siliconized-nylon shell that fits over a 50–70 L pack and stuffs into a pouch sewn to its own hem. At 113 g, it is aimed at hikers who want rain protection for the outside of the pack without carrying a fully fledged waterproof pack liner. The trade-off is price: retailers list the medium at about $54, a lot of money for four ounces of nylon.

Key Specs

Spec	Detail
Weight	113 g (4 oz)
Fits pack volume	50–70 L / 3,000–4,300 cu in
Packed size	10.5 x 7.5 cm (4.25 x 3 in)
Fabric	30D Ultra-Sil siliconized nylon made with CORDURA yarns
Construction	No-seam body
Water repellency	Non-PFC DWR on the outer face
Extras	Keeper strap across the harness, drainage hole at the base, attached stuff sack
Warranty	Sea to Summit lifetime guarantee

Performance

Waterproofing. The cover’s main selling point is what it lacks. Most pack covers are sewn from several panels, and every stitched seam is a place for water to get in. Sea to Summit makes this one without seams. A single piece of siliconized Cordura does the work. The silicone is impregnated into the fabric rather than laid on as a coating, so there is no waterproof layer to peel or abrade. Sea to Summit says the fabric weighs about a third as much as traditional coated nylon. A Trailspace reviewer used the large size through a 30-day John Muir Trail hike with rain on 10 of those days. The reviewer reported no leaks, including when the cover protected the pack overnight.

Durability. Cover-on, cover-off is the real test. On that JMT trip the cover went on and off at nearly every stop and held up. The reviewer described it as durable for what it is. That qualifier matters. Thirty-denier ripstop is not armor, and it does not belong in a bushwhack through catclaw, but on maintained trail it has a good record. Owners rate it well. The manufacturer’s page shows 4.8 out of 5 across 35 reviews, and Cabela’s shows 4.7 across 26.

Fit and wind. A keeper strap pulls the cover snug across the harness, and an elasticized edge holds the lower hem. Owners report the cover stays put in wind. It also fits roomy packs: the JMT reviewer ran the large over a 75 L-class pack with a foam pad strapped to the back and found the fit comfortable. The cover is not a complete seal. In heavy, wind-driven rain, water can still reach the gap between the back panel and the harness. The cover protects the pack body and its contents, not the shoulder straps or back panel. Anyone carrying a down quilt in a pack with no liner should still use a liner or dry bag. A pack cover is a first line of defense, not a replacement.

Weight and packed size. The weight comparison is mixed. Against a trash compactor bag or a sheet of Tyvek, 113 g is a heavy item. The JMT reviewer put “heavier than some of the (makeshift) alternatives” in the cons column. Against heavier polyurethane-coated covers, the Ultra-Sil is substantially lighter. It compresses into its attached sack to 10.5 x 7.5 cm, which slides into a lid pocket or side pouch. The attached stuff sack also means it cannot be left behind at the trailhead.

Drainage and care. A drainage hole at the base lets water run out rather than pool when the pack is set down. Sea to Summit recommends hand washing with mild soap and lukewarm water. Air dry it completely before stuffing it, because a damp nylon pouch left in the bottom of a pack becomes a mildew risk.

Pros & Cons

Pros

• Seamless body removes the leakiest part of a typical pack cover
• 113 g and a 10.5 x 7.5 cm packed size, with the stuff sack attached
• Silicone-impregnated finish does not peel or flake the way a coating can
• Keeper strap and elasticized hem keep it secured in wind
• Drainage hole at the base
• Strong owner ratings: 4.8 out of 5 on the manufacturer’s page
• Backed by a lifetime guarantee

Cons

• Retail price around $54 is steep for what it is
• Heavier than a trash compactor bag or a sheet of Tyvek
• Does not protect the back panel or shoulder straps in driving rain
• Thin fabric is better suited to trails than to brushy off-trail travel
• Not a substitute for a pack liner for items that must stay dry

Who Should Buy This

This is for the backpacker with a 50–70 L pack who wants a cover that is easy to use, rather than something to fiddle with. It suits hikers in wet climates such as the Pacific Northwest, the Appalachians, and the Scottish Highlands. They want to keep the pack fabric from soaking up water and gaining a pound or two of weight. It also suits anyone who uses it on and off all day and wants a cover that will survive that kind of handling.

Skip it if you have a pack made of Dyneema Composite Fabric or other non-absorbent material. Those packs gain little weight from rain, and a liner alone is the lighter system. Skip it, too, if your pack is smaller than 50 L or larger than 70 L, because Sea to Summit makes other sizes for those. Hikers who are strictly counting grams will prefer a liner and no cover at all.

Verdict

The Ultra-Sil Pack Cover is among the lightest purpose-built pack covers you can buy, and the seamless body is what makes it work. It earns its place for hikers who spend real days in rain and want a cover that survives repeated use. The price is high, and a liner is still necessary.