Sea to Summit Ultra-Sil Compression SackSmall - Yellow Sea to Summit Ultra-Sil Compression Sack - in stock now. The Sea To Summit Ultra-Sil Compression Sack is a compressible sack for organizing and shrinking the gear inside your pack. Haul your sleeping bag, extra clothing and more with an ultralight, compressible sack that takes up less space. Pack it up, roll the top and clip it shut, then utilize the 4 compression straps on the exterior to bring down the size. Available in five different sizes plus a few different colors. Products on Sale Are Discontinued Styles or Colors. Features of the Sea to Summit Ultra-Sil Compression Sack 4 straps for even compression Extra long straps so these sacks can really be filled to capacity Bar tack reinforced stress points Pull handle on the bottom Slippery finish for easy packing.