C18: probably short for obsolete cant togemans coat, from Latin togatoga + -mans, of uncertain origin
a unit of thermal resistance used to measure the power of insulation of a fabric, garment, quilt, etc. The tog-value of an article is equal to ten times the temperature difference between its two faces, in degrees Celsius, when the flow of heat across it is equal to one watt per m²
1708, "any outer garment," shortened from togman "cloak, loose coat" (1560s), thieves' cant word, formed from French togue "cloak," from Latin toga (see toga). Middle English toge "toga" (14c.) was also a cant word for "coat."