The Ultra-Sil Pack Liners from Sea to Summit are extremely useful companions and are available in different sizes. A large, inexpensive dry bag that protects your clothes or provisions from rain and when crossing rivers. Also suitable to store it overnight outside the tent. The Pack Liner is made of 70 denier fabric just like the classic Dry Sacks. Ultra-Sil: a very light waterproof nylon fabric. The outer shell is surrounded by a silicone layer; the inner layer is PU coated.