Sea To Summit says:

The Air Stream Pumpsack is a versatile, easy to use and ultralight mattress pump that also doubles as a 20 litre dry sack.

The Air Stream is our big-volume sleeping mattress pump, it's based on our 20L Ultra-Sil Nano Dry Sack, with added valve plug and foot loop. The 20 Litre Air Stream can be inflated with a single breath. Two to three cycles from the Air Stream are enough to fill most sleeping mats, so you're ready to go quickly, with minimal breath condensation in your mat or dizziness from blowing the mat up. The Air Stream can be used as a 20L dry sack or ultralight pack liner.