The Avian Envelope page Omit the Rhino Tough-Tear fabric section Fabric All Avian envelopes are constructed from 1.9 oz. per square yard 100% rip stop nylon. We have used this same basic fabric since our conception in the Fall of 1974. From our pleasure flyer/sport competitor to our heavy-use/commercial operators, our fabric has repeatedly proven itself in the air and on the ground.