Footwear is an inseparable gear during physical activity; however, it compromises with one critical aspect of the human body: heat regulation and sweating. Thus, footwear breathability comes into question as an important factor in balancing comfort and performance, especially in a hot and humid environment. Current findings, despite still limited, have discovered negative effects from poor breathability in athletic performance across different sports. Additionally, wearing less-breathable footwear is one of the major contributing factors in increasing risk of diseases and foot-related injuries. Under such circumstances, sweat management and lack of footwear breathability is one major caveat within the shoe design, however, the pathophysiology is still academically understudied. To date, there are very little to no publications that comprehensively discuss about this topic, and findings are inconsistent across numerous perspectives, making the puzzle mostly unfinished. In contrast, the running industry has been conducting independent and/or commercial research and development programs which explores variables in shoe design related to breathability. Reflecting from it, authors discuss on the importance of conducting further academic exploration in this topic while proposing several potential studies to begin with, to bridge the gap and develop a better understanding.

• Heat
• Sweat
• Humidity
• Thermoregulation
• Footwear Upper Materials

Putra JC, Nagano H, Watanabe K, Rakwal R (2025) Footwear Upper Breathability: An Understudied yet Critical Aspect for Physical Activity. JSM Foot Ankle 6(1): 1054.

Experts concur that adequate breathability should be one of the important footwear features in a qualitative [1], and quantitative Delphi study [2]. Academic research related to footwear breathability, particularly in running where the lower limb biomechanics is dynamic and repetitive, is deemed important, however, found to be insufficient [2,3]. Currently, the discoveries of the relationship between footwear breathability and its impact on human locomotion are still scattered or incomplete. It is understood that poor breathability affects the microbiome growth inside a footwear, a source of odorous smell [4], but does not mention the contributing factors leading to it. Another research also found that shoe fitting influences breathability in non-breathable footwear material such as leather shoes [5], however, their findings did not mention the effects of friction between the plantar surface and the insole for oversized shoes, which hypothetically can generate heat and increase sweat rate.

With limited to no ventilation, consequences from long-term usage of poor breathability footwear can lead to collateral damage, by the increasing risk of injury and foot-related disease. To safely endure the harsh working conditions, importance of footwear breathability may be often underestimated, resulting in higher prevalence of diseases and musculoskeletal or movement-associated injuries (such as tripping, slipping, etc.) [6]. On the other hand, foot-related diseases such as tinea pedis has been identified as one of the highest risks resulting from poor footwear breathability [7]. The prevalence ranges between 23% on the general population (non-athletes), 22-31% on runners and 43-64% on general athletes (unspecified field of sports) [8]. It is even higher on military personnel, particularly men, ranging from 34.8% on armor officer trainees to 81.5% on advanced infantry trainees [9]. On immunocompromised population or patients with diabetes and peripheral vascular diseases, untreated and/ or prolonged tinea pedis can lead to complications such as cellulitis, secondary bacterial infections, pyoderma, osteomyelitis, and in the severe case, may coalesce to amputation [10].

• All this requires further investigation about footwear breathability and its impact. The objective of this study is to propose research directions guided by the current findings and fundamental questions arising from the practical aspects:What are the influencing factors of footwear breathability,

• What can be done for the industry to create more innovations on this matter,

• What can be recommended for the general population.

Footwear and Thermoregulation

Thermoregulation mechanisms play a central role in maintaining our body temperature homeostasis at 36.5 37ºC. This whole chain of regulation is controlled in the hypothalamus, which acts as the “central command”, where afferent sensory inputs such as heat and cold are perceived through peripheral (skin epidermis and dermis) and visceral thermoreceptors [11]. In terms of heat, thermoreceptors deliver the signal to the hypothalamus, which activates physiological mechanisms to achieve temperature homeostasis through radiation, evaporation, and convection. One of the evaporation mechanisms is sweat production (perspiration), in which heat is bonded with our bodily fluid and carried away to be excreted through sweat glands scattered across the skin [12,13]. This mechanism varies at an individual level, depending on age, gender, presence of tattoos, medical conditions [14 16], the structure of sweat glands [17,18], and hydration status [19] which all can influence perspiration rate.

The foot is no exception to this mechanism, which is illustrated in Figure 1 [20].

Figure 1: Bodily sweat distribution across sections [20] (reproduced with permission from Smith CJ, Havenith G. Eur J Appl Physiol. 2011).

The comfortable foot environment also has a narrow window, ranging from 28 34ºC and 60-65% relative humidity level. Slight deviation from this range can increase the risk of adverse effects such as profuse sweating or overheating in high temperature [21,22]. Therefore, maintaining adequate breathability is a logical standpoint. Maintaining constant evaporation is vital during exercise. For non-breathable occupational footwear, such as construction worker safety boots, firefighter shoes, etc., risks of overheating sharply rise.

Current Understanding

Breathability plays a role in controlling several interrelated factors of the foot environment: humidity and sweat production, temperature, odor, overall comfort and impact on biomechanical factors and associated performance. Breathable shoes allow moisture to escape, keeping the inner environment relatively similar to the outside. This factor can be influenced by the material choice of the shoe upper and insole, which in detail goes to its design and engineering [4,23–25]. During the COVID-19 pandemic, use of personal protective equipment (PPE) during long-hour shifts was a tremendous challenge for heat management (trapped caloric radiation with less chance of escape) among healthcare workers [26]. This phenomenon brought a sign that breathability has a direct effect on comfort in clothing, including footwear [27]. In sports, the choice of material determines the effect, be it apparel, footwear, or protection gears, these are all designed and engineered with some amount of breathability and quick-drying features. Nevertheless, no studies have fully assessed effects of materials used for sporting gears from multi-dimensional perspectives [28]. It is also difficult to create a mapping of how each material affects its breathability in real-scenario experiments.

Thermal radiation as a byproduct of energy expenditure on the foot is another issue that can be tackled by increasing footwear breathability. Overheating can be prevented during hot-humid days and sweat can be dissipated during colder days. Several studies in material science have mentioned that the choice of material does affect breathability in terms of thermoregulation [29-31]. In cold weather, poor breathability insulation materials can lead to sweat accumulation inside the clothing environment. If the wicking properties of the fabric reaches its limit, accumulated sweat will reduce the temperature of the insulated environment, leading to frostbites or even hypothermia in severe cases [32].

Odor management is also closely related to the amount of breathability in the shoe upper and midsole. High perspiration rate and humidity resulting from poor breathability generates a friendly environment for the foot microbiome to thrive and sustain [33]. This can be felt by the increase of odor production as a byproduct of the bacterial metabolism inside the shoe and can be temporarily overcome by sprays, perfumes, or fresheners. However, that does not solve the problem primordially, re-emphasizing the importance of shoe design in its prevention [25].

Breathability also can unexpectedly affect footwear performance. Temperature rise is an immediate consequence of poor breathability, and may affect midsole softness of a shoe [34]. Midsole softness has a major influence on running biomechanics, affecting the whole feel of the shoe itself. This is not a crucial matter for occupational shoes, as most of the midsole is made with firmer materials. Softening in higher temperature was observed on running shoes that incorporate Non- Newtonian (NN) material such as foams containing Poly(ether-block-amide) (PEBA), Ethylene-vinyl-acetate (EVA), etc. as the material of midsole construction [35].

Breathability and functionality can often be compromising trade-off features. A study stated that comfort was the most important feature for football footwear. However, the design and engineering has not yet successfully accommodated those expectations, contributing to impaired sense of comfort and increased risk of injury for football players [36]. Based on these findings, functionality of a type of sports footwear can sometimes contradict with other variables, which result in omitting one feature to preserve the other. Requiring more ventilation and opening, breathable footwear materials can be a negatively-affecting variable for footwear durability and shape integrity. Eventually, the findings reported in these researches concur that footwear breathability is a vital feature that needs to be taken into account in terms of design and engineering. Despite such, there is still a lacking strong, comprehensive academic standpoint to highlight the importance of breathability on comfort and improvement of quality of life.

As stated above, problems related to lack of footwear breathability have been acknowledged in numerous studies, however, publications regarding experiments on its contributing factors and effect are very minimal, scattered, and incongruent. Breathability testing in the industrial sector has been using methods that does not involve human activity (such as ISO 9237:1995, SATRA TM47, wind tunnel, smoke tests, etc.) [24,37,38]. Methodological assessment of how it affects the physiological and biomechanical properties is also lacking. Especially, the variability of sweat rate, what affecting factors contributing to it, as well as the footwear material and design are still not fully understood. To date, there is no gold-standard method on how to assess breathability, therefore using the existing variables and to discover a strong association with it will be necessary as the initial step. Here, authors have decided to look into this ‘unsung’ importance of footwear breathability and would like to propose an idea towards a comprehensive understanding: bridging scattered information and filling the gap, linking it into a full concept about this feature and its applications in a large population scale (Figure 2).

Figure 2: The current understanding of cause and effect of footwear breathability.

This figure illustrated the causative relationship between variables that could be found and rearranged from this paper. It is also stated that there is still a huge gap in nearly all sorts of variables, ranging from the causative effect such as the shoe parts which are heavily involved with breathability, such as shoe upper and insole, as well as its impact on the human foot and the shoe itself. The effects are still unknown, at what extent breathability acts as a determining factor, and studies exploring more into this topic is highly appreciated. In addition, the effects on human body be it physiologically or biomechanically can also be assessed. Despite there are several researches that incorporates breathability as their main study objective, the full understanding in relation to alteration of heat thermoregulation process is still not fully understood. Also, authors propose a pilot experiment to initiate the research as a first step in this project (Figure 3).

Figure 3: The proposed pilot experiment research design.

To conduct a meaningful and standardized data collection, the authors propose a diagrammatic scheme on the methodology to collect data related to footwear breathability. There are several key factors that needs to be incorporated into the whole experiment design. First, is the presence of adjustment period. In this stage, the environment target for each study needs to be determined, as breathability can be observed differently in different environmental settings. Secondly, subject needs to undergo the acclimatization process, to ensure the body’s metabolism is adjusted to the temperature, humidity, and wind speed desired for the experiment. Third, is the presence of controlled exercise. It is recommended that the exercised is prescribed at an individual level, determined by each subject’s fitness level referred from the pre-screening tests. Standardized training intensity can reduce the bias, as well as analyze the data in a more careful manner. Lastly, is the data collection period post- exercise; this process is critical since metabolism changes after exercise occurs, and perspiration rate may be altered at this time. Effects of materials can be closely observed at this period.

Pioneering through running, sensors, and clear protocol

The development of the top-tier road running shoes has been incorporating amazing engineering and designs recently, which plays in role to increase footwear breathability. However, most of the market road running shoes (“daily trainers”) are still developing various upper material combinations which each are trying to find the balance between comfort, support, and breathability for users. The difference between these “supershoes” and the daily trainers and other footwear for other purposes are substantial that the relevance of assessing its breathability is imminent. Progress in this field has been rapidly growing for the past decade, and given the array of options in running footwear design and engineering, it can provide a stepping stone to understand on a human-based controlled experiment protocol. Current sensor development which has the ability to collect valuable data such as internal footwear temperature, relative humidity, and perspiration rate. Thermal sensors, thermocouples, thermography, helps to visualize the thermal changes inside the footwear environment [24,25,39]. Relative humidity and perspiration may illustrate human influences better, however, the technological development of such sensors are still limited [40-42]. Given the current progress, it is an opportunity for researchers to initiate studies based on this existing platform, which can be made as a milestone to explore further.

Future Work Awaits

Qualitative studies using larger numbers of subjects can be an initial step in mapping out the necessity in a broader spectrum, as well as to get a specific picture on a specific group of population in general and sport populations. Clinical surveys where immunocompromised patients, or patients with complicative diabetes in hospitals can be part of the first qualitative studies to assess how it affects the group, and what solution can potentially be provided to alleviate the complications. The second study focuses specifically on the sports population. The idea is to have large groups of athletes to participate in a clinical survey, assess the demands and bridge the gap between the consumers’ (athletes) needs and solutions therein. In addition, other sports which have poorer footwear breathability such as football, basketball, winter sports, or speed-cycling can also be understood from its ergonomics, aerodynamic effects, in relation to breathability, therefore incorporating this feature will not act as a trade-off for other crucial features related to the game’s performance.

For occupational footwear, where breathability is generally compromised, a study to fully understand the physiological intervention in the current environment can be the initial step towards further exploration to solve this ever-lasting problem. Authors propose that, if materials that can act as a safety feature, as well as providing breathability can be developed and tested in a randomized controlled trial manner, issues related to occupational foot-related diseases can also be diminished. For example, incorporating absorbent as the main material in insole development which can hypothetically act to reduce humidity on an enclosed footwear environment, would provide some amount of relief for safety occupational footwear such as military boots, construction shoes, or firefighter shoes.

Another momentum to align shoe development with the latest technological advancement can also potentially be carried out, for example, utilizing the ever-developing machine learning through artificial intelligence (AI) in development of shoes. To fully develop this feature, the understanding of the current technological availability as well as its reliability in research methodology is required, which can be done by conducting researches involving rich datasets to assess footwear breathability from specific point of variables (such as heat, humidity, sweat rate, etc.). This has a great potential to illustrate the conditions inside the footwear environment and how breathability interventions can alter the findings, which, if succeeded, can be modified and adjusted to the footwear design and engineering, embedding multiple sensors into the structure, and provide real-time data from real activities. Data collection of such parameters can provide big-data analytics about footwear breathability, and can potentially act as a preventive method for users, or as an accurate assessment tool that can analyze individual data at high accuracy.

Given that possibility, it is hypothesized that breathability can act as a strong advantage point for footwear companies to develop new innovations in part of capturing the demand on the targeted market segment. Authors envisage tremendous possibilities and a full understanding of breathability would not only benefit the academic field itself, but also can be applied into a broader socioeconomic spectrum, affecting large groups of population, benefiting all stakeholders in the process.

The  lead  author  thanks  Tsukuba  International Academy for Sport Studies (TIAS2.0) for providing endless assistance, supervision, mentoring, and connecting between stakeholders in different fields of expertise in sports science and medicine in discussing this understated field of academic research.

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