When it comes to thermal comfort, the head is one of the most sensitive body parts. According to studies, the head is responsible for up to 1/4 to 1/3 of total body heat loss in warm climates, although it makes up only 7-10% of the body’s surface area. The head contributes most strongly to the perception of overall body comfort, especially in warm conditions.
One of the most common reasons bicyclists give for not wearing helmets is the discomfort and excessive heat that helmets create. A recent study among German helmet users indicated that 57% of them complained about excessive sweating – far more than impaired visual field (9%) or perceived head pressure (10%). Other factors certainly play an important role, such as design, convenience, vanity, social perception, cultural norms and fashion. Similar results were found in the survey conducted by Working Group 2.
The bottom line is, cyclists are not likely to wear a helmet that is uncomfortably warm. Dramatic improvements can be made in helmet design, based on scientific, state-of-the-art developments in thermal comfort. More comfortable helmets can potentially increase helmet use among bicyclists.
Working Group Focus
In relation to COST Action TU1101, the primary focus of Working Group 4 was to:
Produce an overview of the scientific state of the art, including suggestions for future directions for thermal aspects of helmets;
Create models and experimental simulations to help in Research and Development of more thermally comfortable bike helmet designs;
Contribute to guidelines, directives and norms for both testing helmets and regulating their production;
Investigate new materials and helmet forms to determine optimal design and minimal thermal discomfort;
Test new helmet designs and their thermal properties;
Establish project initiatives to improve thermal aspects of helmet design. Information & Communication Technology (ICT) also plays a role in this;
Improve thermal comfort for cyclists who will eventually wear the helmets.
Through literature review, scientific modelling, experimental simulation and real-world testing, Working Group 4 has not only been able to establish a core set of guidelines and testing protocols, but has made the first steps towards viable solutions. In fact, two additional research projects have already engaged with researchers from this Working Group. The results have clear implications for both the design and creation of better, more comfortable headgear.
Implications for Industry
The results of Working Group 4’s investigation have direct implications for the bicycle helmet manufacturing industry. The output offers ways to accurately and effectively monitor and model thermo-physiological responses. This, together with psychological considerations, can result in headgear that is better accepted by prospective users.
The two factors that have a strong impact on the thermal properties of helmets, and consequently on overall thermal comfort, are wind speed and body posture. Helmets must therefore be adjusted for the type of cycling activity. In addition, improved radiant shielding properties contribute to overall comfort, and several design improvements are offered to optimise this effect. These improvements also include the adjustment of inlet and outlet air vents, and the air channels that connect them, to further improve air convection capabilities.
Working Group 4’s output shows that different methodologies, including computational modelling, can help in the development of new and effective helmet design, while experimental simulation can provide proof of concept and optimisation capabilities. Furthermore, the possibility of adding active cooling systems to helmet design were explored. Dynamic vents or active cooling systems that regulate heat loss can be controlled by models that predict thermal comfort at the head, so as to optimise thermal comfort in the design stages.
Implications for Legislators
Legislators can play a key role in both the establishment of industry standards and the increase in helmet-wearing compliance. A multitude of studies indicate that thermal comfort is a primary factor in whether or not bicyclists wear helmets. Therefore, the conclusions drawn by Working Group 4 that indicate ways to increase thermal comfort are key to overall compliance.
Furthermore, legislation that provides minimal design requirements regarding heat transfer in helmets, in addition to protective properties, will improve manufacturing and encourage usage. However, care must be taken to avoid over-regulating the designs, as this inhibits innovation.
Working Group 4’s output provides methods for the evaluation and assessment of thermal properties – both ventilation and radiant shielding. With these new parameters, thermal property information can be made available to customers. This can assist in customers’ evaluation of wearer comfort, and influence their buying decisions. Thermal properties will therefore become a direct priority for manufacturers, and they will maximise thermal comfort in future helmet designs.
Standardisation of Test Methods
Studies show that the current methods used by manufacturers to assess cooling capacity and thermal comfort include some parameters that are not relevant, and subjective feedback from wearers, which is not enough to effectively assess the effectiveness of different cooling methods.
Working Group 4 has therefore provided the initial ideas to begin developing a standard for assessing cooling effectiveness. These standards will allow for accurate and consistent testing of products, and will help make thermal comfort a direct priority for manufacturers. It will also allow manufacturers to clearly, objectively and accurately inform customers about the cooling effectiveness of various helmet types. This will help influence buying decisions.
In turn, standardisation of testing and modelling methodologies would allow legislators to regulate the production of helmets within the comfort-level boundaries necessary to encourage helmet usage among citizens. And, it will allow for comfort levels to be incorporated into legislation, along with safety standards.
Creating the modelling framework
Of course, many factors contribute to the perceived comfort of helmets. Parameters like outdoor temperature, exposure duration, level of activity, clothing characteristics and the helmet materials and thermal properties all impact thermal comfort. Taking all of these factors into account, Working Group 4 was able to develop a method for simulating, predicting and assessing thermal comfort in bicycle helmets. Further recommendations have been made to improve local head sweating models, the biophysical testing of a helmet’s thermal properties, and of course, human trials on head perspiration. The results of similar tests are already being used to evaluate thermal comfort in other body regions, as well, and can have implications for clothing and equipment development.
Using the methods set forth from Working Group 4’s output, helmet manufacturers can create accurate models to simulate, test and assess the comfort levels of various helmet designs, and more quickly and accurately achieve better results in achieving more comfort for helmet wearers.
The next development involved modelling that could accurately assess core body temperature in relation to metabolic activity and skin temperature, with the goal of real-time, overall body temperature management (thermoregulation). The results indicated that core body temperature could be accurately modelled, based on actual data, using either metabolic activity alone, or the combination of metabolic activity and skin temperature. These models, based on empirical data, can also be interpreted in a mechanistic way, and compared to a more sophisticated model, such as the ‘Fiala thermal Physiology and Comfort’ (FPC) model. Of course, overall core body temperature control is a key factor in dynamically predicting perceived comfort when wearing protective headgear.
Combining mathematics and manikins
For the first time ever, mathematical models of human physiology have been combined with a single body part manikin to establish a more accurate and complete evaluation of thermal comfort. In this way, comfort can be assessed under dynamic conditions, such as varying outdoor temperature, clothing and activity levels, and provide a coherent physiological control. This model performed well when predicting the overall physiological response under changing conditions.
The advanced thermal manikin headform at Empa.
Industrial Application: Testing Helmets on the Market
In a broad and multi-faceted investigation, a number of factors were addressed related to the reasons why bicyclists in Europe do not wish to wear a helmet. Chief among them were design, the problem of mussed or matted hair, the social perception of helmeted bicyclists, the lack of convenience involved in carrying and storing a helmet, the lack of thermal comfort, and increased heat/sweating. Although studies show that helmets do help keep cyclists warm in cold weather, the fact that helmets are not compatible with other clothing was a deterrent.
Working Group 4’s investigation included an evaluation of bicycle helmets currently on the market. Several designs and helmet covers were tested for their ability to transfer and dissipate local heat accumulation. Using head manikins, a variety of testing scenarios resulted in data related to convective cooling (through proper air flow) and radiant shielding (protection from direct sunlight). The differences in convective heat loss were measured. The areas of the head most affected by radiant heat were determined, and the ways in which helmets can actually drastically increase heat loss were determined.
Innovative Design Solutions for Ventilation
To dig even more deeply into the possibilities, a group of design students developed various new and innovative helmet designs, attempting to surpass the thermal comfort capabilities of the helmets currently available. The designs were tested against factors like wind speed and the affect of hair on ventilation. In the end, the ability to customise helmets for specific user needs became the most effective solution.
The tested helmets with codes and authors’ names
Some of the helmets designed in this experiment performed better in practically any condition, as compared to helmets currently on the market. In more than half the cases, the new designs performed better than the best helmets currently on the market.
However, more research is necessary to put these results into full context. It proved difficult to find a single new design that performed well in multiple factors. The best helmet design for sweat evaporation was not the same as the best helmet design for insulation. This indicates that bicyclists’ solutions must be defined by the user’s bicycling activity, weather conditions, speed of travel, etc. In addition, at this point in the investigation, the protective factor of the various designs was not taken into consideration, and could affect final designs. However, there was a clear indication that the new designs developed during the investigation could significantly improve helmet ventilation, as compared to helmets currently on the market.
Already, the research conducted by Working Group 4 has captured the attention of the industry. The results and findings were used as a catalyst for the involvement of members of the Working Group in two other key studies, namely:
- INTHEL.COM: A study aimed at improving the safety of electrical bicycles (e-bikes) through the development of an intelligent helmet system;
- SmartHELMET: A project that brings together academic partners and industry representatives to develop safer, smarter and more comfortable helmets, which will contribute to helmet acceptance and increased bicycle use.
Potential for further study
Based on available literature and Working Group 4’s output, the areas with the greatest potential for further development in improving thermal properties of headgear include:
- Modelling of the head’s sweat rates;
- The effect of hairstyle on forced convection;
- Development of active control systems for improved thermal comfort;
- A laminar system that creates an optically closed surface relative to the radiant source;
- More actively combining thermal knowledge to impact overall knowledge.
In addition, each individual facet of Working Group 4’s investigation resulted in advice and proposals for further study and inquiry, including:
- Modelling framework: Improving and validating applied models;
- Managing thermoregulation: Managing thermoregulation in real time;
- Head simulators: Defining the physiological limitations and validating the coupled system in a wide range of exposures;
- Thermal properties of bicycle helmets: Improving global dry heat loss through better design;
- Design solutions for ventilation: Selecting the best of the innovative new solutions and continued impact testing, as well as model development.