These cotton "long-johns" were worn by astronaut John Glenn during his Mercury mission in February 1962.
The garment was worn under the spacesuit, and the trilok "spacers" were to provide a small space between the skin and suit to permit the movement of air throughout the suit.
The Hanes Company manufactured and B.F. Goodrich modified them. NASA transferred the underwear to the National Air and Space Museum in 1967.
Transferred from NASA - Manned Spacecraft Center