A birth control means designed to limit sperm production by effecting a slight temperature increase in the testes comprises a scrotum insulator cut from a flat sheet of a flexible insulating material to the shape of a trapezoid. Preferably the insulating material is a moisture impervious plastic film vacuum metallized to have an infrared reflective surface. The scrotum insulator is used by being held in place around the scrotum preferably as by insertion in unmodified jockey-type shorts.