The durable Hero Rubber + Nike Grind Ninety Collection offers 90% Nike Grind by weight, delivering the highest level of recycled rubber from athletic shoes in each square foot of material. Each square foot of Ninety is manufactured with the recycled rubber from five athletic shoes. This rubber flooring is crafted without recycled tires or crumb rubber, making it a super clean product.it is approved for areas with free weights when using 8mm thickness or greater. It's available in square tiles and interlocking tiles. Size options - 24"x24"Square/Interlocking, 24"x36"Square, 38"x38"Square/Interlocking, 48"x72"Square/Interlocking