If I'm reading Laile's page correctly, http://www.laile.co.jp/jpn/products/.../guard_sb.html
, the Beatrush undertray is 5.00mm thick duralumnium (http://en.wikipedia.org/wiki/Duralumin
). FWIW, of course.
Edit...just spent some time here, http://item.rakuten.co.jp/laile/s5up60160/
, which is saying it is 2mm thick not 5mm. Perhaps the "rally" version is the thick one they were referring to, http://item.rakuten.co.jp/laile/a560161/#a560161