Gap filler is a term used to describe materials used to fill in gaps between two surfaces. The most common gap fillers are SHIM, SEALANT, PUTTY, and denim. A SHIM is a thin piece of material used to fill small gaps between two surfaces. SEALANT is a material used to fill larger gaps between two surfaces and create a waterproof seal. PUTTY is a soft material used to fill gaps between two surfaces and can be easily molded. Denim is a type of fabric that is often used to fill gaps between two surfaces.