Ideal for visual stimulation, examining size relationships, and exploring natural, tactile, and other detailed materials found inside or in nature. Mirror Blocks are stacking hardwood frames with inset Double-faced Mylar windows--ten pc. set in assorted shapes: 4 rectangle, 2 square, 2 triangle and 2 half circle shapes. They can be used to enhance indoor and outdoor STEM-based activities. Standard unit block measurements so they are great to use with other block playsets. Smooth, rounded corners and edges fabricated for safe handling.