What's the difference between a water-resistant and a waterproof compression sack?

Water-resistant sacks (like the budget Frelaxy and Hikenture models here) shed light rain and splashes but are not submersion-proof. Waterproof compression dry bags, such as the Sea to Summit eVac line, use welded seams and a roll-top closure to keep gear dry in heavy rain or a tipped canoe. Expect to pay considerably more for a true waterproof sack.