The development of the airtight and heat-resistant membrane is an important factor to realize the low ballistic coefficient reentry spacecraft with flexible aeroshell. The air tightness is necessary for the inflatable structure and the heat-resistance against aerodynamic heating is also demanded. The candidate of the membrane is Zylon[○!R] (Toyobo. Co. Ltd.) and it can endure more than 600 degree Celsius. Authors tried to give Zylon airtight property with coating on it, but the coated sample was not airtight. If polyethylene is used as an inside layer of Zylon, the two layers system have the airtight property. As outer layer should be a heat shield in this case, radiative heat transmission test of membrane is also tested. Thicker Zylon and Zyron with Kapton[○!R] film show less transmission rate than Zylon.