In the 1990’s. In the early 1960’s tights were introduced as leg ware. While young adult college students wore them for a time, they were seen as too casual and youthful for older women working in offices. Young girls who were not old enough to wear big girl grown up sheer hosiery wore them in large numbers, especially in the 1970’s. One piece pantyhose debuted in 1959 but since women’s hemlines were at or below the knee, the garter straps attached to girdles or garter belts were safely hidden from view so pantyhose did not find an audience until mini-skirts became popular.
In the 1990’s, opaque tights were again introduced for grown women & this time large numbers of women embraced them, wearing them under skirt suits, dresses, & skirt separates worn with a blazer. This time around (perhaps because more women than ever worked in an office setting), dress codes were modified and tights as office leg ware became accepted.
Because pantyhose & sheer two piece stockings are fragile, tights were happily welcomed as a more economical (longer lasting) alternative to sheer hosiery. Women who tended to put runs in their pantyhose while running around in the morning hurriedly getting dressed were happy that the thicker tights lasted longer. Tights were also warmer, not just in the winter but also in the summer when certain office settings felt like a deep freeze because the air-conditioning was cranked up full blast.