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The most useful resource I found while investigating phase change materials was the following paper which explores several different types of low temp salt based PCMs: https://www.researchgate.net/publication/316893824_Preparation_and_thermal_properties_of_Glauber's_salt-based_phase-change_materials_for_Qinghai-Tibet_Plateau_solar_greenhouses
The key to reducing the melting point of a PCM is to make what is called a eutectic mixture ( https://en.wikipedia.org/wiki/Eutectic_system ). In this case that is a mixture of two different hydrated salts. When the two come together the freezing point of both is lowered to a temperature which depends on the particular salts used and the ratio between them. Sodium sulfate and table salt (sodium chloride)
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Below are ebay affiliate links (I will receive a small commission if you make purchases through affiliate links):
Sodium sulfate: https://ebay.us/4JoC8V
Calcium chloride: https://ebay.us/kcniPG
Ice pack cooling vest: https://ebay.us/WZqhHo
Sodium acetate hot packs: https://ebay.us/pLjYz8
Reusable silicone bags: https://ebay.us/o4lnvk
Referenced videos:
Radiative Sky Cooling Playlist: https://www.youtube.com/playlist?list=PL1a2HkcVbmAWExiWT__qQypLEwkvijnIM
Reinventing Starlite: https://youtu.be/0IbWampaEcM?si=8mIY9GgNNKFdKsLG
Solar balloons: https://youtu.be/0QL_Ijxs9fk?si=-NekRaVpQ2ao2zf4
Wax fabric: https://youtu.be/HedRbIsM75M?si=5NjcRvY-3qu3__J2
Second channel: https://www.youtube.com/channel/UCb6Y8DZRfg80q6ng3Ca2xYg
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