I bought them in all colors and from different stores, the sizes vary a lot but they come out big or small but they are fine and they have a plastic smell at first which goes away very quickly.

Bad quality Chinese rubber. The smell of synthetic rubber is unbearable! I don't know how toxic materials have been used, but I washed them and left them in the sun to air out and the smell remains! I got redness on the parts where the upper part of my foot rubs. You get what you pay for, and it would be better to choose better quality than this..