Bullard’s revolutionary Isotherm technology offers unparalleled cooling power, helping to reduce the chance of heat-related illnesses that sometimes occur in today's difficult work environments. Specially engineered to maintain a constant 55ºF, the Isotherm® cool vest will provide cooling for approximately two and a half hours. The cool vest uses an interchangeable front/ back cool pack system and is fully adjustable. The Isotherm® cool vest comes in dark blue and is large only. Ship. wt. 2 lbs.