... , in & out are different shape for each, 4cm size, make up differ building. 1. circle,heart, square & ... rubber material, which is recycle plastic, more safe for kids too, ASTM F963 & CE standard, Phthalate ... different color will be available.4. in & out for each shape will be different, circle in & bear ... different building shape, a good kind of building block.6. a good kind of intelligence goys for kids ...