Complex sentence: Polypropylene and polyester geosynthetics have also been used for this purpose and in some northern countries, a layer of polystyrene boards have been used to delay and minimize frost penetration into the subgrade.
Split into simpler sentences: Polypropylene and polyester geosynthetics have also been used for this purpose. A layer of polystyrene boards have been used to delay and minimize frost penetration into the subgrade.