Sea to Summit Ultra-Sil Stuff Sack

The Sea to Summit Ultra-Sil Stuff Sack is a basic organizational sack made from 30D Ultra-Sil nylon with a DWR finish, offered across a 1.5–20 L range — anything from a small pouch for odds and ends to a full sleeping bag or down jacket sleeve. At just 16 g for the size reviewed here, carrying several sizes at once barely registers on a pack's total weight. The DWR coating makes the fabric shed light rain and splashes, but this isn't a fully waterproof product — the seams aren't taped, so submersion or sustained rain will eventually let moisture through. Anyone needing guaranteed dry contents, such as electronics or a sleeping bag in genuinely wet conditions, needs a proper welded-seam drybag instead. In practice this is a compression and sorting tool rather than a waterproofing solution. For that role — keeping gear grouped and preventing a pack's contents from spilling out at every stop — it does the job reliably and at almost no weight cost.