Cooling vests and other cooling accessories to be worn under ventilated jackets will help keep you comfortable in extreme temperatures. Most of these products work by soaking the garment in water, letting it absorb as much as possible, giving it a quick wringing out, and then donning and wearing under your ventilated outer gear. The Rev’It Cooling Liquid vest above claims a four- to six-hour period in which the product slowly lets water evaporate to help keep you cool. There are several manufacturers making similar items. Rev’It also offers cooling collars, wristbands, and zip-in liners for specific jackets.