These cute studs is my graphics transferred to a special polymer and then covered with resin for durability and extra shine. 
 
The slipper is made of HYPOALLERGENIC steel (Surgical stainless steel. Hedgehog dimensions: width x height x depth approx .: 12x10x1.5 mm. and each piece may be a little different from what you see in the picture, the material is a bit unpredictable, but that's what makes them original :-)