Men's slides are handmade from a sheared Turkish carpet or from wool kilims. The uppers are wool and the insoles and soles are leather making these a sustainable shoe. And yes, slides are often called mules or slippers they are all the same shoe built without the hind quarter.
Our slides will stretch as they are worn. The wearer's heel should be at the end of the insole but not hanging over. Tap your toe and the foot will sink deeper into the shoe. If before they are broken in your foot is too far into the shoe it will be difficult to wear when broken in. As the insole gets a little wear [dirty] the slides will be easier to keep on the foot.
You are about to buy the most comfortable slide you have ever owned and a slide that is a one of the kind shoe.
BTW We have never had a pair returned because they didn't stretch!