Second, the PCM product must be effective, offering good heat transfer. Otherwise, it is no better than common gypsum drywall. The three principal PCMs investigated for use in phase change drywall are salt hydrates, paraffins, and fatty acids. Other PCM applications commonly use salt hydrates. Since they absorb moisture, which decreases their effectiveness, salt hydrates require costly and impractical encapsulation, with a semi-impermeable coating for improved performance.
Paraffins are waxes.
They are readily available, inexpensive, and melt at different temperatures relating to their carbon-chain length. Paraffin can be incorporated into drywall in two ways, by direct immersion and by adding permeated plastic pellets to the drywall mixture during the manufacturing process. Since drywall is a porous material, it can absorb melted paraffin when immersed in it. Extra paraffin runs off, leaving no buildup of wax. Immersion times vary depending on the amount of PCM uptake desired, however, they rarely exceed ten minutes.