The S-XL Inflation Dry Sacks are compatible with the Light Mattress, Flex™ Mattress, and Base Mattress valves. The XS Inflation Dry Sack is compatible with the Flex™ Air Mattress and the Ultralight Mattress.
Note that all mattress except the Base Mattress come with an Inflation Dry Sack. Only purchase one if you are looking for a replacement or want one for your Base Mattress.
The Inflation Dry Sack is compatible with the Flex™ 3D Mattress valve but those mattresses come with a different style of inflation storage sack already. No need to purchase one for your Flex™ 3D.