Scoobies Silicone Stackables are 100% Silicone, BPA Free, Latex & Phthalate Free. These Stackables Silicone toys are incredibly durable, easy to clean, and can be used for countless sensory-based activities like stacking, sorting, and nesting Silicone rainbow Stackers are less predictable when stacking than the wooden ones Due to the extreme flexibility in the nature of silicone, pieces may bend to slide while stacking, creating a more challenging experience and adding to the overall fun and excitement of play.