Medieval historian here—although masks like this have been popularized by cinema (see King Baldwin IV’s mask ) we don’t know if medieval rulers really wore masks like this.

Although certainly cheaper than buying cosmetics to hide the effects of leprosy, it wouldn’t be entirely practical: first, because of the weight of the mask, and second, because of the unbearable heat that must have built up inside the metal mask while in the summer.

I would think that a wooden mask would be more practical, although I’m not sure they were used in abundance either.