# Evaluation of Snowboarding Helmets in Mitigation of the Biomechanical Responses of Head Surrogate
## 2 Materials and Methods
### Snowboarding Helmets  
In this work, three types of medium-sized snowboarding helmets were evaluated, one conventional and two equipped with anti-rotational technologies: a multi-directional impact protection system (MIPS) and a wavy cellular liner (WaveCel). Figure 2 shows photographs of each helmet, and Table 2 tabulates the details of each helmet. The conventional helmet consisted of an outer shell, impact mitigation liner, and comfort liner. The MIPS helmet consisted of an additional plastic sheet that was loosely tethered between the impact mitigation liner and comfort liner. This sheet was designed to reduce the rotational motion as it underwent sliding (slip) during impact. In the case of the WaveCel helmet, the \begin{table}
\begin{tabular}{c c c c c c c} \hline \multicolumn{5}{c}{**Human Head Substructure**} & \multicolumn{5}{c}{**Corresponding Surrogate Material**} \\ \hline \multirow{4}{*}{\begin{tabular}{c} Skin \\ \end{tabular} } & **Density** & **Elastic** & **Long-Term Shear** & **Density** & **Elastic** & **Long-Term Shear** \\  & **(kg/m3)** & **Modulus** & **(MPa)** & **(kPa)** & **(kg/m3)** & **Modulus** \\  & & & & & & **(MPa)** & **(MPa)** \\ \hline \multirow{3}{*}{\begin{tabular}{c} Skin \\ \end{tabular} } & \multirow{3}{*}{1004–1544 [47]} & \multirow{3}{*}{0.42–0.85 [48]} & \multirow{3}{*}{-} & Silicone rubber & \multirow{3}{*}{1080 a} & \multirow{3}{*}{0.60 a} & \multirow{3}{*}{-} \\  & & & & & & \\  & & & & & & \\ \hline \multirow{2}{*}{\begin{tabular}{c} Skull \\ \end{tabular} } & \multirow{2}{*}{1270–2274 [47]} & 1230–5380 & \multirow{2}{*}{-} & Polylactic acid & \multirow{2}{*}{1250 b} & \multirow{2}{*}{3166 b} & \multirow{2}{*}{-} \\  & & & & & & \\  & & & & & & \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} Dura \\ mater \\ \end{tabular} } & \multirow{2}{*}{1050-1550 [47]} & \multirow{2}{*}{10–40 [51]} & \multirow{2}{*}{-} & Thermoplastic & \multirow{2}{*}{1111 c} & \multirow{2}{*}{27 c} & \multirow{2}{*}{-} \\  & & & polyurethane & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Brain \\ \end{tabular} } & \multirow{2}{*}{1001–1620 [47]} & \multirow{2}{*}{-} & 0.4–1.4 [52], & \multirow{2}{*}{10\% gelatin} & \multirow{2}{*}{1060 [44; 54]} & \multirow{2}{*}{-} & \multirow{2}{*}{1.3–3.5 [55; 56; 57]} \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\ \hline \end{tabular} The head surrogate material property values are taken from the literature and data sheets. \({}^{\mathrm{a}}\) From data sheet—[[https://www.smooth-on.com/products/dragon-skin-30/](https://www.smooth-on.com/products/dragon-skin-30/)]([https://www.smooth-on.com/products/dragon-skin-30/](https://www.smooth-on.com/products/dragon-skin-30/)) (accessed on 6 July 2024). \({}^{\mathrm{b}}\) From data sheet—[[https://forward-am.com/material-portfolio/ultrafuse-filaments-for-fused-filaments-fabrication-ffff/engineering-filaments/ultrafuse-pla-pro1/](https://forward-am.com/material-portfolio/ultrafuse-filaments-for-fused-filaments-fabrication-ffff/engineering-filaments/ultrafuse-pla-pro1/)]([https://forward-am.com/material-portfolio/ultrafuse-filaments-for-fused-filaments-fabrication-ffff/engineering-filaments/ultrafuse-pla-pro1/](https://forward-am.com/material-portfolio/ultrafuse-filaments-for-fused-filaments-fabrication-ffff/engineering-filaments/ultrafuse-pla-pro1/)) (accessed on 6 July 2024). \({}^{\mathrm{c}}\) From data sheet—[[https://www.ultrafuseff.com/product/ultrafuse-fpu-natural-85a-175](https://www.ultrafuseff.com/product/ultrafuse-fpu-natural-85a-175) mm-750g/]([https://www.ultrafuseff.com/product/ultrafuse-fpu-natural-85a-175](https://www.ultrafuseff.com/product/ultrafuse-fpu-natural-85a-175) mm-750g/) (accessed on 8 July 2024).  
\end{table} 
Table 1: Material properties of human head substructure and corresponding surrogate material reported in the literature. conventional impact mitigation liner was replaced by the wavy cellular liner that provided both impact mitigation and relative sliding capabilities.