QUILTED DOUBLED LAYED POLY COTTON; ZIPS DIRECTLY INTO THE INTERNAL ZIPPERS IN THE ALPHA II; 3 ZIPPERED WINDOWS PLUS SKY LIGHT (INSULATION LINER REQUIRES INTERNAL ZIPPERS TO INSTALL. PLEASE CHECK THE INSIDE OF YOUR ALPHA FOR COMPATIBILITY. OUR FIRST-GENERATION TENTS DO NOT HAVE THE INTERNAL ZIPPERS REQUIRED FOR INSTALLATION.)