Craters on the Moon are caused by asteroids and meteorites colliding with the lunar surface. Craters on my felted slippers sneakers are caused by my hand from natural wool and silk. Can by made of softest natural gray merino wool from Australia, they gently massage feet, or natural a little rougher Goland/iceland wool mix from Europe. Felt is a natural and renewable material, made natural, organic, not dyed wool, using just hot water and soap – one of the purest processes in textile.Warm feeling on a cold day and cool on a hot day due to insulation properties of the wool fibers, it is extremely wear proof and warm. These slippers feel like a second skin on your feet.