A common material for the Substrate of a PCB A particular advantage of this material is that it's thermal expansion characteristics are close to those of copper tracks See also FR4
Fibreglass is a material made from short, thin threads of glass which can be used to stop heat escaping. fiberglass a light material made from small glass threads pressed together, used for making sports cars, small boats etc. or glass fibre Fibrous form of glass, developed in the 1930s. Liquid glass issues in fine streams through hundreds of fine nozzles, and the solidifying streams are gathered into a single strand and wound onto a spool. Strands can be twisted into yarns, woven into fabrics, or chopped into short pieces and then bonded into mats. Glass filaments and yarns add strength and electrical resistivity to molded plastic products. Glass fabrics are used as electrical insulators and as reinforcing belts in automobile tires. Discontinuous fibres are formed into wools, mats, or boards, commonly used in buildings, appliances, and plumbing