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:
A less expensive and less bulky alternative to traditional dry bags. You can squash these into spots ordinary heavy dry bags won't go. Fits into little corners of a sea kayak or light enough to take backpacking or adventure traveling. Suitable to keep contents dry in any wet situation where the bag is not submerged.