Work out how much Glass you have by weight and multiply by 2.5. i.e. for 2kg of fibreglass mat, you will require 5kg of resin. Alternatively, use our Materials Quantity Calculator. Roofing applications may require more resin if the resin is applied to OSB3 boards as the boards will soak more resin. Our materials calculator will give exact requirements depending on application e.g. Roofing, Pond Lining or General Fibreglass Projects.