Genuine Isopon GFM – Fastglas Glass Fibre Mat. TheIsopon Fastglas Glass Fibre Mat provides a strong, durable and weatherproof solution for repairing or reinforcing a variety of substrates. TheIsopon Fastglas Glass Fibre Mat is designed for use withFASTGLAS Resin and Hardener to create a tough, lightweight and weatherproof repair.