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 and 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 and 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 a