When building small model aircraft, it is often necessary to provide an insulation barrier between a PCB and other components or between a PCB and a metal frame. That insulation barrier must be thin, light and puncture resistant.
And sometimes you must prevent a nearby screw from cutting through heat-shrink tubing or wiring insulation
So what is the best material?
I have found that old credit cards or old gift cards or stolen hotel key-cards are absolutely excellent. They are thin, lightweight and very puncture-resistant.
They are readily obtainable and can be cut with scissors or drilled, and most (flexible) glues will stick to them as well. If you look at my aircraft, you will probably see a Mileage Plus card under the flight controller, or as protection for the ESC wires.
When I check out of a hotel, I always have two new fresh cards to use for my "builds".