ADD ABOUT 6 layers of fiberglass, I found this nice netting that is made for fiberglass resin so I alternated between the traditional fiberglass sheets and the new fiber-netting. According to JL Website I need 15.57 L of volume, with the packing peanut method I ended up with about 15 L I will add poly fill to make up the 1/2 liter I shorted the sub.