John, I use drafting mylar with 3M double sided tape. Clear sheet protectors have been used too. Frankly, I don't think it makes our planes go any faster, but it might reduce the throw required for a given response rate, and then only if there are conventional hinges, and not live skin hinges, which are the norm on high performance models today. I sure wish someone would try some telemetry experiments with, and without "gap seals". I think it's just one of those "feel good" features. That's my opinion on internal push rods too! Enough of my ramblings.