Outlast blocks will not warp, shrink, twist or rot, and do not need covered storage, whatever the weather. 100% safe for children. 27 pieces. Weatherproof wood? Outlast products are made of acetylated Accoya wood, which has been proven to last for several decades in direct contact to the ground. Leave it outdoors in any weather. Extremely durable and environmentally friendly, it is the perfect wood for your outdoor classroom.