Mama-san. Please inject more sense into your daughter.
@JumboWheat01
They are widely used. You can see bundles of them in Uniqlo alone. Just kinda new within the decade and half or so though, and the warmer places don't use them much. It's just used as a 'plot device' in this chapter hence the... 'newness' of the heattech.
Compression stuff is "under wear" in a literal sense that it can and often is worn under other clothing, but it isn't underwear. Plenty of guys and girls wear just compression stuff, at least in my area.