The Sea to Summit Air Stream Pumpsack is an ingenious large sized sleeping mattress pump which doubles as a dry sack to minimise your pack load As a pump simply connect the pump to the mattress valve & place your foot on the loop From at least 30cm above inflate the dry sack in one breath then seal the bag using the roll top closure & push the air into the mat Due to this excellent use of the Venturi effect most mattresses can be inflated in just two or three breaths so repeat if necessary As a dry sack this bag is based on the Sea to Summit Ultra-Sil reg Nano dry sack & has a 20 litre capacity a roll top closure & is fully seam sealed for an extra water resistance making it a fantastic ultra-lightweight dry sack for storing your belongings in or as a vacuum bag for your down sleeping bag when you are backpacking This Pumpsack is an excellent way of being able to double up the use of some of your kit & thus save on pack weight by using this dry bag to pump up your camping mattress then you will be able to put up your camp quickly easily & with minimal stress so you can get on & enjoy your time in the great outdoors