# Superinsulation Materials for Energy-Efficient Train Envelopes
## 4 Results
### Application Aspects  
Silica aerogel boards can be handled similarly to mineral wool: they can be cut, drilled and bent. These operations do release dust, however, so pre-cutting to the desired dimensions for installation in the train is preferable. VIPs, on the other hand, cannot be cut or drilled and have to be handled with care in order to prevent any damage to the envelope. They can be bent to a certain extent but less so compared to silica aerogel boards. Furthermore, for the installation location, it has to be made sure that there are no sharp edges or protrusions that could damage the envelope during the installation or the use of the train--especially given the continuous vibrations during operation. Hence, from the handling point of view, VIPs are best suited for even surfaces that are protected from mechanical stress as well as rectangular areas. While openings in VIPs for penetrations (fixation elements, etc.) or more irregular shapes can be realised during production, this increases cost, making it less attractive. Aerogel boards, on the other hand, can be handled flexibly, also allowing for higher dimensional tolerances, as they can be cut to size on site. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **MARHE (kW/m\({}^{2}\))** & **CFE (kW/m\({}^{2}\))** & **D\({}_{8}\)(4)** & **VOF\({}_{4}\)** & **Flame Spread** & **Surface Ignition, Flame Spread** & **CITG** \\ \hline Requirement for & & & & & & & \\ R1 HL3 & \textless{}60 & \textless{}20 & \textless{}150 & \textless{}300 & \textless{}150 mm & \textless{}150 mm & \textless{}0.75 \\ \hline Silica aerogel & & & & & & & \\ board & & & & & & & \\ \hline VIP with fire & & & & & & & \\ protection sheet & 31.9 & 49.4 & 57.1 & 74.30 & No ignition & No ignition & 0.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the fire tests for the silica aerogel board and the VIP with a fire protection layer. Each measurement is determined with three samples. Values given represent mean values. From the thermal performance point of view, VIPs are superior to aerogel boards, with a thermal conductivity including aging of about half of that of aerogel boards, as shown above. This is the case, though, only for panels of sizes larger than 300 \(\times\) 400 mm\({}^{2}\)[41]. For panels of a smaller size, the thermal bridge constituted by the edge of the panel affects the performance too much, so that the use of small panels is not recommended. Both aerogel and VIPs are significantly more expensive than conventional insulation materials, with a cost at around 5500 and 6500 EUR per m\({}^{3}\), respectively, depending on purchase volume and manufacturer. This compares to the cost of several hundred euro per m\({}^{3}\) for conventional materials. Considering the cost per performance, to reach, for example, a U-value of 0.2 W/(m\({}^{2}\cdot\)K), the cost would be approximately 220, 500 and 40 EUR/m\({}^{2}\), for VIPs, silica aerogel and conventional materials, respectively. Thus, the application of these superinsulation materials is economically only justified if the desired insulation performance cannot be reached with conventional materials, i.e., due to space restrictions. As VIPs have a lower thermal conductivity than aerogel boards, their cost per insulation performance is roughly half of that of aerogel. Hence, if in a given application area, all other parameters are equal, VIPs are preferable from an economic point of view. This cost advantage is based on a sufficiently high number of items of VIPs, though, as VIPs can be produced more cost-effectively if more units are produced. Hence, for a single area of a given size that does not repeat at all, aerogel boards may still be more cost-effective. The environmental product declarations (EPDs) of VIPs and silica aerogel boards are summarized in Table 4 with their global warming potential and the non-renewable primary energy. The values for melamine resin foam are listed for comparison.