That depends on what you’re using it for. For practicing rolls, cartwheels, or extra cushioning for calisthenics, a mat that’s soft but not too thick – between one and two inches – is best. For mats that have a polyurethane foam core or bottom layer, ask about the mat’s indentation load deflection/indentation force deflection (ILD/IFD). The higher the number, the firmer the foam.