My Skin Seems Thicker Than Most?

Literally. I'm not fat, I'm skinny, but today while I was fooling around with my friend Emily, I noticed her arm skin, was more stretcher then mine. And then I notice, her skin was also a lot thinner then mine. I started to realize, a lot of people's skins are thinner. I don't get it. Why is mine so thick and tough, when I'm skinny like anyone else..