The World’s Warmest Jacket The MegaWarm jacket is the ultimate LifeLabs innovation, giving you the warmth you need at the top of a mountain or on the coldest winter days in the city. Fully waterproof and remarkably light for its scale and coverage, the MegaWarm Jacket defies common standards for insulated apparel. With the highest CLO rating of any jacket in existence (9.25), MegaWarm is the planet’s warmest jacket.