Complex sentence: Tempered hardboard is hardboard that has been roller coated with an oil the oil is than a primer for the clear polyurethane varnish which go on both sides of the board this gives it more water resistance, impact resistance, hardness, rigidity and tensile strength.
Split into simpler sentences: Tempered hardboard is hardboard that has been roller coated with an oil. This gives it more water resistance, impact resistance, hardness, rigidity and tensile strength.