Our Phase Change Crown Cooler (PCCC) attaches easily to hard hat liners to keep you cool on the job. Phase Change Cooling Packs deliver a constant temperature of 58 degrees Fahrenheit for up to two (2) hours. Reusable, non-toxic and non-flammable. Includes one (1) 1" x 6" diameter circular Phase Change Pack. Pack does not require a freezer! Can be chilled in ice water; refrigerator or freezer optional. Great for use in the field when freezers are not readily available. The cooling performance is not impacted by humidity or outside temperature. The extra pack is a great value! Keep in the freezer or a cooler, ready to use. Lightweight: weighs less than 1 lb. Attaches easily to hard hat liners with hook and loop tabs. Unisex and discreet design. Blue. One size fits all.