Underlayment Options Sport Court Indoor Athletic Flooring always come with a rubber underlayment system. These underlayment options have a wide range of thicknesses for shock absorption, varying from 15% - 45%. You can customize your indoor floor with your choice of underlayment. Most recreational rooms don't require any more than our 1.5mm underlayment. Once you start getting into basketball, volleyball and other competitive sports, the 3.0mm and 5.0mm rubber underlayments are ideal. If you are retrofitting an older floor, the 3.0mm and 5.0mm thicknesses provide a solid overlay for your existing surface. Any small imperfections in the sub-surface will, for the most part, be absorbed by the Sport Court rubber underlayment. Contact us today to discuss which underlayment option for your indoor gym floor project will work best!