Can Mormons wear regular underwear over their temple garments?

Sure. So long as the temple garment is worn properly, anything may be worn over it. Most Church members don't want to wear regular underwear (aside from women's bras) over the temple garment because it just adds extra bulk.

Sure. So long as the temple garment is worn properly, anything may be worn over it. Most Church members don't want to wear regular underwear (aside from women's bras) over the temple garment because it just adds extra bulk.