FLEXA's Sleep System The unique, flexible FLEXA slat system is specifically designed for kids. Each slat is made from 6 layers of birch veneer for maximum strength and durability. The slat system works together with our mattresses, creating the FLEXA sleep system. Slat system and mattress combined contour with the weight of the body - aligning the spine at a perfect angle. Not only does this benefit the child sleeping in the bed, it is also great for the parents because they will have well-rested kids in the morning.