Because Millboard’s core consists of a combination of plastic and polyurethane reinforced with fibreglass; it is very stable compared to wood or wood-based composites. The unique closed ‘cellular’ internal structure makes the board light and strong. The solid planks will therefore not expand, shrink or warp. We do recommend a 4 mm gap between the sides of the boards and a 1 mm gap between the ends of the boards. A 10 mm gap should be left between the boards and every fixed surface to facilitate drainage.