Abstract: Reversible quadrangular mats of similar construction are provided, defining a grille section on one face and a flat section on the opposite face, and interlocking edgewise joints to edgewisely releasably interlock the mats in coplanar fashion. These joints include thicknesswise grooves made at the peripheral side edge sections of each mat, defining two upturned edgewise lips in two adjacent grooves and two downturned edgewise lips in the two other grooves. The mats are made from a semi-flexible material. One side lip of a first mat is frictionally engageable into one side groove of a second mat, for their interconnection.