Heavy fiberglass mat

[gw204f]

On exposed surfaces, make sure your layup consists of one or more layers of CSM just under your finish coat of gelcoat/paint/etc. The CSM helps to prevent print-through of heavier cloth/biax and if you are laminating from the inside out, you will be doing your final sanding/grinding on the mat instead of on the long fibers of the cloth/biax.