Crawler Innovations was the first to combine closed cell and open cell foam into one package. The Lil’ Nova Foams have been around since the beginning and are made from the best compounds available. The Lil’ Nova Dual Stage Foam design is for all high-performance applications where grip and traction are essential. Available in a variety of compounds and sizes, the Lil’ Nova Crawler Foams are the perfect addition for your new tires. Sold as a pair. These inserts feature a Standard Cut, closed cell inner foam, with a Soft conventional or open cell density outer foam. The closed cell inner foam is super dense, water proof, is not temperature sensitive and is extremely durable. The conventional outer foam is not temperature sensitive, but it is not water proof. The "Standard" inner is flat between the area where the outer and inner meet. This is the original design inner and it supports the most weight, but it is not as responsive on the rocks for competition rc rock crawling. The 4.50" is the Middle Size inner in the Lil' Nova Dual Stage foam line and designed for 1.9 tires and heavier rc vehicles. Please watch our video for a complete explanation of the Lil' Nova Foam System. Approximate size: 4.875" Height x 1.75" Width