The New POL-C500MII modular Polar Cover has a thick layer of padded insulation and is lined with Mylar® fabric to reflect heat back towards the camera.  Air-activated heat packs (PHP-2 sold separately) can be inserted into interior mesh pockets for extra heat during extreme cold-weather shooting. 
Insulated-protection is also provided for the LCD viewfinder, which can be quickly accessed under a Velcro-sealed cover.   There's also a shotgun mic protector and a lens-hood to prevent condensation on the lens when returning indoors. The new modular design works for either standard lens or matte box.