Top Flite MonoKote is a plastic film. It is leakproof, and won't let air pass through the film. When you try to apply one piece over another, any air trapped between the two pieces will show up as a bubble. There are basically two ways to prevent this:

1) Use an erasable marker to draw the outline of the trim piece. Starting about 1/8" inside the mark, poke lots of pinholes in the covering below. Very carefully iron-on the trim piece.

2) If the trim piece is large, start 1/8" inside the borders of the trim piece, and cut away all of the material underneath. Carefully iron-on the trim piece. When you go to shrink the trim piece, lay pieces of wet, rolled-up papwer towel on the seam. That will keep them from becoming loose while the rest of the area is heated. Make sure you apply the trim piece as wrinkle-free as you can. When you iron it on, some wrinkles will develop, but they'll go away when you shrink the middle. Large, multi-colored designs have been done this way.

The "Windex" method works for MonoKote Trim, because it has adhesive that doesn't need to be heated. If you use this method for regular heat-activated MonoKote, residual moisture between the pieces will vaporize and can cause bubbles.

With extreme care, and slow application, MonoKote can be applied over MonoKote without air bubbles, but this usually only works for fairly narrow pieces.

If you do get bubbles, they can be eliminated almost invisibly by *****ing them with a pin and then using a heat gun. The air will expand inside the bubble, and escape out of the pinhole. The colored adhesive will fill the pinhole for almost total invisibility. Heating with an iron doesn't work quite as well.