I’d think they’d be breakable, because they’d be slamming against pavement, cement, etc. with every step, with hundreds of pounds of pressure slamming down with each step, but that’s just my theory.
With modern technology? Maybe. There’s a lot of conflicting information available regarding whether or not one could actually walk (or run) in a modern glass slipper. But more importantly, it wouldn’t have been possible in 1697. The whole point is to illustrate how dainty Cinderella is.
One theory is that the word “glass” is a mistranslation, another is that it is a satire on Louis XIV’s obsession with fancy footwear. Whether this is true or not I can’t imagine that glass slippers would be comfortable to wear and might easily lead to Cinderella being carried from the ballroom on a stretcher.
If you notice on the website, nobody is actually wearing the shoe. The photo shows a man starting to put one on a woman’s foot. These shoes are made as props for a photo shoot, and they sell a display box. The shoes can be sold singly or as a pair.
Glass is actually pretty strong. It’s just that if there’s a little crack, it will propagate all the way across. A glass slipper would probably be wearable if a resilient sole was added to prevent little chips from forming while walking on hard surfaces.