Young Brunette Girl Wearing A Black Hold-ups On The Table

The thickness of thigh-highs is measured in Denier, the same measurement unit used for different varieties of feminine stockings.
History
With the invention of nylon, thigh high stockings took center stage in women's fashion. While high-end consumers never lost their fascination with silk thigh highs, their nylon counterparts were so ubiquitous that they ended up baptizing the entire stocking family. In popular use, stockings were referred to as 'nylons' in the '40s. It was in the 60's that thigh highs retreated towards a more marginal place in women's fashion. It is accepted that the popularity of the mini-skirt was an important factor in this. As the skirt was growing shorter-and-shorter, revealing the top-line of the stockings silently was relegated to the realm of the osé. Pantyhose gained in popularity.