The Xpack-70-200 PL is a unique temperature transition control pouch designed for a 70-200 f 2.8 lens. The unique insulation this pouch offers, means that you can shoot in extreme cold conditions, then wrap up your gear & go indoors without having to expose it to the radical temperature change. The temperature transition will gradually take place while your gear is snuggly protected in the pouch & thus prevent any damaging formation of fogginess or condensation.