Abstract: A fast acting and low leak rate vent for an impact landing bag in which a vent hole is covered by a gas barrier assembly having a flexible membrane and a low gas permeability layer. A flap assembly positioned around the gas barrier assembly includes flaps that are movable between an open position in which the membrane is exposed and a closed position in which the flaps cover and reinforce the gas barrier assembly. An externally actuated flow initiator is associated with a fastening element that retains the flaps in the closed position. Upon landing, the flow initiator is activated to sever the fastening element and release the flaps and the low gas permeability layer. Thereafter, the internal pressure within the landing bag under landing forces causes the membrane to burst, releasing a flow of gas from within the landing bag to attenuate impact.