Neck Cooling Tube Wearable Cooling Neck Wraps for Summer Heat I Cold Gel Ice Pack | Reusable Neck Cooler Commute and Outdoor Activities | Relief for Hot Flashes or Fever The filling material of neck cooler is engineered phase change material (PCM). Both inorganic PCM and organic PCM have been used in this application product. Bio based normal paraffin PCM and bio based PCM are used as organic PCMs. A easy way to differentiate PCM type is by their density. Inorganic has a bigger density around 1.4 while 0.77~0.78 for normal paraffin pcms and 0.82~0.84 for bio based pcms.