When added to polyester or epoxy resin, Block Surf’s Q-Cell Filler thickens the resin to make it more workable and expands it to fill in large areas. This expansion reduces the amount of resin required therefore reducing weight. Q-Cell is only a filler and should be sealed with a coat of resin before use. Blocksurf Q-Cell Filler for surfboard repair. Q-Cell Filler is great for filling in large voids, drys white and is easily sanded. Mix with resin to preferred thickness and apply as needed.