Premium Wood Walnut 46" x 46" - no Lip 3/8" Thick Chair Mats Traction backing keeps mat in place on any surface (carpet or hard floor) and protects it from chair movement. 3/8" thickness ensures this wood chair mat won't crack, dimple, or break. Green Product - the wood fibers come from sources certified by the Sustainable Forestry Initiative (SFI) and have been awarded Greenguard Certification. The total recycled content by weight is 65%. A "lip" is the tongue that extends from the mat which protects the area just under the desk. The dimensions of mats listed below with a lip are the total size of the mat, inclusive of the lip. This chair mat is not recommended for use with hard-ball casters or metal wheels.