Sea to Summit have used high performance 70D waterproof fabric to balance durability with weight, with a roll top closure and fully taped seams they are the classic all purpose Drybag.
Sea to Summit says:
Flexible in both senses of the word—our Lightweight Dry Sack is soft and pliable and also ideal for many different uses. It is made from a lightweight 70D waterproof, durable Nylon fabric so you can squash them into spots heavy-duty dry bags won’t go. The interior polyurethane coating is coloured white to improve visibility and make it easy to find small items in poor light. They use the same non-wicking roll-top closure as our other dry sacks for a reliable watertight seal. Featuring a D-ring at the field repairable buckle point for easy attachment, they’re ideal for backpacking, cycle touring, travel, ski touring and more.