The Stikit refill roll system is designed for your comfort and utility. The blocks are made of tough plastic for long life and durability.They allow you to sand into corners with the flat end and into curved or contoured areas with the rounded end. When the abrasive on the surface is used up, simply peel back the used portion, and pull down on the roll end to expose fresh abrasive. The abrasive used is silicon carbide coated on an A wt. paper backing with a load resistant coating.