Eleven phase change materials (PCMs) for cooling humans in heat-stressed conditions were evaluated for their cooling characteristics. Effects of packaging material and segmentation were also investigated. Sample packs with a different type PCM (water- and oil-based PCMs, cooling gels, inorganic salts) or different packaging (aluminum, TPU, TPU + neoprene) were investigated on a hotplate. Cooling capacity, duration, and power were determined. Secondly, a PCM pack with hexagon compartments was compared to an unsegmented version with similar content. Cooling power decreased whereas cooling duration increased with increasing melting temperature. The water-based PCMs showed a >2x higher cooling power than other PCMs, but were relatively short-lived. The flexible gels and salts did not demonstrate a phase change plateau in cooling power, compromising their cooling potential. Using a TPU or aluminum packaging was indifferent. Adding neoprene considerably extended cooling duration, while decreasing power. Segmentation has practical benefits, but substantially lowered contact area and therefore cooling power.

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Exercising in hot and humid environments can be very demanding for the human body. The next Summer Olympics (postponed to 2021 due to the COVID-19 outbreak) will be held In Tokyo. The average heat and humidity during this period is respectively 35°C and 70 to 80%. This will put the athletes in risky situations due to the rise of the body temperature during the exercise. Goalkeepers in field hockey are especially prone to the heat since they have to wear thick insulating protective gear to keep them safe. A rise in body temperature can deteriorate their responsiveness, raising the chance of letting opponent score. The context of the goalkeeper has been analyzed for this specific weather situation. A set of cooling packs has been produced that can be placed under the trunk and spine area of the body protector, and under the sweatband inside the helmet. Compromises had to be made to satisfy the comfortability, mobility, cooling duration, safety and ease of use. The mobility of the goalkeeper had to stay as high as possible, therefore only spots were chosen that were already covered by an existing piece of protective gear. Insulating material has been added to one side of the cooling packs so that the user can choose for higher or lower intensity cooling depending on their preference. The active cooling duration for each cooling pack is no longer than half a match in order to keep the packs as light as possible. The packs thus had to be easily replaceable since they have to be replaced during halftime. The compartments of the cooling packs had to be connected to the surrounding compartments, allowing the cooling liquid to flow away during impact, resulting in higher durability of the product. The holes that connected the compartments could not be too wide, since the liquid would flow down due to gravity, resulting in uneven distribution of the cooling liquid throughout the pack. To help resolve this last issue, a thickening agent has been added to keep the cooling liquid distributed evenly. All materials inside the cooling packs are non-poisonous in case the cooling pack would fail for any reason. Multiple phase change materials have been tested. The final designs are filled with a mixture of ethanol, water, carboxymethyl cellulose (for an increased viscosity) and an edible blue coloring agent to give the perception of cooling. The trunk and head packs are sealed using a heated aluminum mold. The back cooling pack is sealed using a laser engraver. The trunk and head cooling packs have been tested on impact under the protective gear according to European regulation and could be manufactured and used immediately. The Back cooling pack has not been tested on impact since there is no regulation to protect the back of the goalkeeper. Under normal use this pack would also not fail.