## 5 Conclusions  
Existing motorcycle helmets generally provide an adequate performance level in terms of protecting the head during impact. However, even the most sophisticated and expensive of helmets are ineffective when not actually worn. Many studies have shown that wearers in hot climates tend to dispense with helmets for comfort. Thus, during the design of a motorcycle helmet, it is necessary to consider not only the protection afforded to the rider, but also the level of comfort. Accordingly, this study proposes a novel open-face helmet design in which three parallel ventilation slots are incorporated into the upper-head region of the helmet structure. The impact performance level of the proposed helmet was compared with those of three traditional helmet designs (full-face, open-face, and half-face helmets), by simulating free-fall drop impact tests at a speed of approximately 6 m/s. The results obtained in this study support the following conclusions:  
1. Of the three traditional helmet designs (full-face, open-face, and half-face helmets), the half helmet resulted in the greatest peak headform acceleration (303 G), whereas the full-face helmet resulted in the lowest acceleration (197 G). Thus, although the half-face helmet can provide the greatest degree of user comfort, because of its lighter weight and better ventilation, it offered the poorest head protection performance out of the three designs. Notably, however, all of the three helmets were seen to satisfy the Snell standard (300 G) and DOT standard (400 G) for the maximum headform acceleration. 2. The peak headform acceleration of the open-face helmet (235 G) was just 19% higher than that of the full-face helmet (197 G). Thus, if the additional protection afforded to the chin and frontal-face area of the rider in the event of an accident is disregarded, an open-face helmet provides both a good level of protection, and an improved level of user comfort. Consequently, it is a reasonable choice for motorcycle riders in warm climates. However, further research is required to improve the ventilation performance of open-face helmets, in order to enhance the number of riders which are actually wearing them. 3. The proposed prototype open-face helmet with ventilation was observed to result in a lower peak headform acceleration than the original open-face helmet, irrespective of the slot width (8, 14, or 18 mm). The improved energy absorption performance of the proposed design was attributed to the greater freedom of movement available to the liner; this freedom of movement enables the liner to deform under impact, due to the absence of foam in the slot regions of the helmet. 4. Of the three open-face helmets with ventilation slots, the helmet with the slot width of 18 mm resulted in the lowest peak headform acceleration (150 G). However, the acceleration profile for this helmet was observed to have a two-peak characteristic, indicating the partial collapse of the liner under impact, and thus, a lower protection afforded to the head. Therefore, the optimal prototype design was determined to be that with a ventilation slot width of 8 mm, for which the acceleration profile had a single-peak characteristic and a maximum headform acceleration of 160 G.
5. The peak headform acceleration associated with the use of the 8-mm ventilation slot width (160 G) was approximately 32% lower than that of the original open-face design (235 G) and 19% lower than that of the full-face helmet (197 G). Therefore, this confirms the feasibility of the proposed design for motorcycle riders in warm climates. In general, the present results indicate that of all the helmet designs considered in this study, the full-face design provides the rider with maximum protection in the event of an accident. However, comfort is a decisive factor when selecting a helmet for use in SE Asia and other warm climates. Thus, effective helmet design must consider both user protection and user comfort.