Aerodynamic bike helmet!

Step 14 Cut pieces of fiberglass cloth -- enough for 3 layers.

If you've done a lot of fiberglass work, skip the next few steps. Otherwise, here was my sequence: before mixing any epoxy, I took a sheet of fiberglass cloth and draped it over the spackled area I had just sanded. While pressing it onto the surface so that it conformed to the edges of the piece, I drew lines on it so that I would know where to cut. The goal is to cut pieces that won't crease or bunch up when you epoxy them on later. When this happens, it's easy for bubbles to form between adjacent fiberglass layers. For an aerohelmet this may not be a big deal, but such bubbles (called "delaminations") are the subject of much thought and test design in manufacturing scenarios. So, your objective in cutting the cloth pieces is to cut shapes that lie flat against the surface you are working on. Cut as many pieces as you want. I ultimately had three layers of fiberglass -- the underlayer was 20 oz. variety and the next two layers were 7 oz. (these refer to the weight of the cloth per square yard). If you're using the stock fiberglass cloth you can buy at Home Depot, I'd say two layers with reinforcement in the weaker areas (such as the sides) would be a good bet. Or three layers. Both should still be very light and yet flexible enough so that it's easy to remove the final piece from the plug.