Isi Mark For Polyurethane Sole Semirigid ISI Mark is mandatory for Polyurethane Sole, Semirigid as per IS 13893:1994. Polyurethane sole, semirigid, is a type of shoe sole made from polyurethane material. It provides support and comfort, making it ideal for a variety of footwear, including work boots, casual shoes and athletic footwear. Its semirigid nature ensures good shock absorption, slip resistance and lightweight properties.