I have a bottle of clear dope that is fuel proof. They do make another type that is not, but the label on the bottle should tell you. For me, I use it for fuel proofing different parts. The latest use was to fuel proof a built out firewall extension on my Ultra Stick Lite. It helped me keep the wood the same color as the rest of the plane. I could have just as easily painted it a different color with fuel proof paint, but the dope worked for me. As e28m5 stated, it was originally used on tissue paper covered models as a paint since it comes in different colors.