Cool future fashion: Personal cooling as part of social adaptation to hotter climates

“Deadly heat waves: it’s only getting worse”, a headline from this summer, succinctly summarizes recent weather and predictions on its future patterns. According to World Metrological Organization, the last four years have been the hottest on record and the average global temperature has increased by about 1°C (or 1.8°F) since the industrial revolution. Disturbingly, this deceitfully mild increase is mainly due to longer periods of extremely hot weather. While there are uncertainties in climate change prediction, the consensus is that frequency and severity of such heat waves will increase significantly and will do so sooner than previously thought. Regrettably, significant warming will likely occur even if current prevention efforts are intensified, as illustrated in Figure 1 and its caption [1]. Consequently, those of us living in already hot places should begin thinking how our own, as well as future generations’, lifestyles will have to change in response to rising temperatures. Here, I argue that our social adaptation will have to involve the broad use of personal cooling garments and contemplate on what the “cool future fashion” might look like.

Figure 1.

The future is likely to be hotter for many of us, often exceeding the shown temperature and humidity conditions associated with human death, which were identified by More et al. [1] based on global analysis of documented lethal heat events. If the recent Intergovernmental Panel on Climate Change predictions of reaching 1.5°C by 2030 to 2050 occur, twice as many megacities than at present are likely to become heat stressed. This will potentially expose more than 350 million more people to deadly heat. By one further estimate [1], even if strong mitigation action is taken, by 2100 about half of the world population will be exposed to climatic conditions exceeding deadly thresholds for at least three weeks per year. That fraction increases to three-quarters if we maintain the status quo. Furthermore, under this scenario, many densely populated places, mostly near the equator will be exposed to deadly heat for large parts of the year [1].

Life in many hot regions of the world already changes in response to the summer heat. For example, from May to October construction sites in Phoenix, Arizona, are busy long before sunrise, as are hiking and biking trails. Tellingly, the Zoo opens and is busy at six in the morning, but shuts down shortly after lunch, as do construction sites and almost all outdoor activities. However, an increase in the temperature experienced in the early hours, which can already exceed an uncomfortable 32°C (90°F), by just a couple degrees will make shifting schedules ineffective in dealing with the heat. Illustrating what the future may hold, in June of 2018, Quriyat, Oman, experienced a record-high 24-hour low temperature of 42.6°C (108.7°F).

This issue is starting to be acknowledged by many governments. For example, the fourth national climate assessment by the US federal government estimated significant economic losses that will stem from curtailed outdoor work-related activities, while the EU has sponsored a large project focused on heat resilience of workers [2]. Our primary adaptation to the heating climate will be to move as much as possible of the occupational as well as recreational outdoor activities into air-conditioned indoor environments. The inevitable result of this migration will be a soaring reliance on air conditioning that will be difficult to afford for many. Those of us who can afford the prices will be confined indoors for decent segments of the year, which can have negative mental and physical health effects. Imagine a future where going fishing or hiking, taking a stroll in a park, or taking your kids to the zoo is nearly impossible for six or more months each year. Since most of us are likely to find this undesirable, we need to start thinking about approaches that will allow us to maintain not only critical outdoor components of our economic activities, but also some recreational outdoor components of our current lifestyles. Since our physiology will not tolerate these hot conditions, we can adapt to the heat by wearing garments that help cool us.

So what kind of personal cooling garments can we buy today? Aside from fabrics that encourage natural evaporative cooling, we have access to air, liquid, and phase-change cooled garments [3]. As most of these garments are intended for use in highly specialized occupations such as hazardous material cleanup, they are too clunky for everyday use by the public. Moreover, garments that cool through air convection or evaporation are ineffective for hot and humid climates where deadly heat thresholds will often be surpassed. Such garments work well in dry climates but become limited at temperatures above ~40–45°C and can cause severe dehydration. In contrast, the performance of phase-change and liquid-cooled garments is relatively environment independent. Cooling of the former relies on melting of ice or hydrocarbons (e.g. waxes) incorporated into the garments. Illustrating how bulky and heavy these garments are, 1 kg (1 liter) of even the best contender, ice, can provide cooling for half-hour for users who are walking slowly (producing around 200 W [4]) and only for quarter-hour for users who are running at 5 mph (producing around 400 W [4]). Similar concerns apply to liquid-cooled garments, which contain over 20 meters of tubing in just an upper body vest. Encouragingly, use of optimized soft composites as tubing material can reduce the required tubing length three to four times. However, in addition to the tubes, these systems need an external heat sink to reject the heat collected from the body. Typically, these heat sinks are stationary (e.g. large ice-chest), but portable heat sinks that weight around 3 kg have recently been introduced. While these are just two examples of many notable current efforts aimed at improving personal cooling, much more engineering and materials research is required to develop long-lasting, highly-portable, and ergonomic cooling garments. It is also worth pointing out that such efforts would immediately help heat-sensitive part of our population, for example, children, elderly, and individuals with multiple sclerosis. However, in my opinion, if these cooling garments are to be widely accepted it is vital that engineering efforts are integrated with fashion design.

So what will broadly acceptable cooling garments look like in the next few decades and beyond? In the near term, I imagine the trend will be to conceal the cooling components under ordinary clothing comparable to our current fashion. Yet, if the global temperatures continue to soar, fashion might incorporate the cooling as a part of the new aesthetic. From a thermal management point of view, such garments should not only remove more heat, but also help to maintain our core temperature by reducing the internal and external heat loads. For example, metabolic heat generation can be reduced by the use of mechanical exoskeletons; so, we can imagine a future garment that resembles a wetsuit that integrates a conformal soft mechanical support with liquid cooling channels and an easily rechargeable thermal sink. The external heat load could be even further reduced by including adjustable insulation as well as shading and selectively reflective components into the garment. Most likely, such suits will be multifunctional and will incorporate a variety of wearable technologies. Thus, the cooling system will have to manage thermal load stemming from its user, electronics, and the environment.

So what else besides close-fitting “thermo-mechanical wetsuits” might we be wearing in the hot future? Expanding our clothing away from our bodies could have many benefits. In particular, the amount of heat that can be conducted, convected or radiated away is proportional to the heat transfer area (this is why elephants have large, highly vascular ears). Exterior clothing components with a large area could, for example, create effective heat shields as well as heat sinks. Such components could also create micro-climates and provide more space for a robust cooling system as well as a mechanical exoskeleton. I think it is interesting to point out that we would not necessarily have to invent new formats of such garments. Instead, we could follow the “fashion is cyclical” mantra and reimagine, arguably often silly, historic clothing items. Just to provide a few illustrations of such clothing items from the last millennium, westerners wore massive ruff-collars, padded shoulders and sleeves, hoop-skirts, bustles, crinolines, hats and wigs [5]. These clothing items extended far beyond the wearers’ bodies. For example, in King Louis XVI’s France, wired wigs could reach heights of two feet and have enough room to incorporate decorative items such as cages with stuffed or live birds! Undeniably, most of such fashion items were completely impractical, and were the folly of the rich. However, by reimagining the design and with use of modern materials, some historic clothing items could provide cooling functionality that is not achievable with our current, relatively tight-fitting clothing fashion. Could the humble evaporative cooling bandana or towel be outperformed and replaced by an expandable, superabsorbent ruff-collar which could store and evaporate considerably more water (see Figure 2(a))? Could a metamaterial film, that reflects visible light but emits highly in infrared, be incorporated into the surface of an elaborate hat or a foldable calash to enable effective radiative cooling (see Figure 2(b))? Could condenser tubes provide the support for a future hoop-skirt, bustle, or crinoline that would provide large heat rejection area (see Figure 2(c))? These, naturally, are just wild speculations; but besides intensifying preventive measures, I think that it is increasingly important that we start developing better cooling garments that will help us and the next generations cope with the hot future.

Figure 2.

Examples of historic clothing items with large exterior surface area whose format could be reimagined and reengineered to develop novel cooling garments. Specifically, highlighted in blue are (a) a ruff-collar, (b) a calash bonnet, and a (c) cutaway sketch of a cage-crinoline underskirt. These are adaptations of (a) 16^th century François Quesnel’s portrait of Henry III of Poland and France, (b) 1904 Ellen Day Hale “The green calash” painting, and (c) 1856 diagram from “Punch” magazine by an unknown artist. These works are in the public domain in their country of origin and other countries and areas where the copyright is the author’s life plus 70 years or less.

The author would like to thank Professors Maria Wieczynska and Robert Wang as well as doctoral students Kenneth C. Manning and Praveen Kotagama from Arizona State University and Dr. Agnieszka M. H. Rykaczewska from Claremont Graduate University for insightful comments and discussions on the topic.