The traditional Long John’s was a and still is a staple underwear type worn by men. Sometimes it is a one piece outfit made of a waffle weave or similar jersey open weave of actually many types of fabrics. In olden days it was made of wool and primarily worn as a Winter garment day in and day out, as well as the sleeping garment at night. Designed with buttons that ran from the chest to the groin as the means of venting or taking the garment off and on or going to the toilet. It came in a variety of colors. This basic design is still available today.
Along the way, it was decided that a Top shirt and a bottom pants style were also a good choice. Mix or match your colors accordingly. The bottom pants style has a traditional fly in most designs.
AS SPORTS WEAR
With the advent of the polyester fibers of various kinds, a thinner fabric became available with good flexibilities and light weight, yet snug on the body. Welcome to the Polypropylene, Capelene and now nanofiber materials. These fibers are moisture-wicking and provide a degree of insulation when worn as a base layer over other sports gear.