This vest includes four Kool Max Cooling Packs for ultimate cooling and convenient exchange of packs. Smaller sizes use 4.5" x 12" Kool Max Packs and larger sizes use 6" x 15" double-bagged Kool Max Packs. (See Product Features below for more details.) Additional pack sets are offered at a special discount when purchased with the vest! Your choice of an extra set of Kool Max frozen water-based packs or a set of Cool58 58° Fahrenheit phase change packs, which are ideal when freezers aren't available. You may want to order both types of packs for flexibility on-the-go! Full comparison of cooling pack technologies below in the "How Does it Work?" section. Features: Adjustable, Custom Fit: It is important for cooling vests to fit snug to the body for optimal cooling. This cooling vest has adjustable hook and loop straps at the chest, waist and shoulders for a snug, comfortable and customized fit. Convenient And Easy To Wear: Once the cooling vest has been adjusted for size, it is easy to put on every time with the zipper-pull front. The clean design (with no logos or visible pack pockets!) is available in several sizes. Wear the vest over clothing or discreetly underneath. Comfortable 100% Cotton: The cooling vest shell is constructed of durable and machine washable 100% cotton twill. Kool Max Cooling Pack Strips: Kool Max frozen water-based cooling packs require access to a freezer and offer the highest level of cooling energy. These reusable packs deliver comfortable cooling for up to 3-4 hours. It takes more energy to charge these packs in a freezer and in return, the packs offer greater cooling energy than Cool58 cooling packs. (Please note: cooling times are estimates and will vary depending on climate, body metabolism and activity.) The vest includes four (4) 6" x 15" double-bagged Kool Max pack strips. See the size chart for more information. Insulated Pack Pockets: Packs fit into insulated pockets inside the cooling vest. The pockets have a comfortable all-cotton fabric to protect the skin and an insulated outer composite fabric to direct the cooling energy toward the body. Temperature may also be adjusted for comfort by increasing or decreasing the number of clothing layers beneath the vest or the number of packs used. Variable Weight: Size S/M includes four (4) 4.5" x 12" Kool Max Pack Strips for a total vest weight of 4.0 lbs. How do Kool Max water-based cooling packs work?: Kool Max frozen water-based cooling packs require access to a freezer and offer the highest level of cooling energy. It takes more energy to charge these packs in a freezer and in return, the packs offer greater cooling energy than Cool58 cooling packs. These reusable packs deliver comfortable cooling for up to 4 hours depending on environment, activity, and personal metabolism.. (Please note: cooling times are estimates and will vary depending on climate, body metabolism and activity.) Packs are non-toxic and non-flammable. Works in any climate - extreme heat and humidity are no problem! The cooling performance is not impacted by humidity or outside temperature. Specifications: One (1) 100% cotton cooling vest Simple and unisex design with a zipper-pull front. Size is adjustable with hook and loop closures at the chest, waist, and shoulders for a snug, comfortable and customized fit. Packs fit into insulated pockets inside the vest. The pockets have a comfortable all-cotton fabric to protect the skin and an insulated outer composite fabric to direct the cooling energy toward the body. Control the weight by varying the number of packs used. Discreet: can be worn over or beneath clothing. Colors: Blue, Khaki Sizes: S/M, M/L, L/XL, XL/2XL, 2XL/3XL Four (4) Kool Max cooling packs Size S/M includes four (4) 4.5" x 12" Kool Max Pack Strips Polar Products Kool Max Adjustable Zipper Cooling Vest for Size S/M