The main structural armour on Explosion is the Hardox. That's what holds off the spinners and makes it reliable. The purpose of the HDPE is only to cover the gaps in the frame and to absorb impacts, which is why relatively thin thicknesses are sufficient. Also half the reason the HDPE is so tough is the amount of screws holding the panels on. The entire base and flipper arm is made out of Hardox, it needs to be to stop it from tearing itself apart!

Also Ceri it was enough to hold off NST. The damage caused by NST was entirely superficial, and the only reason it stopped in the final was because the link came out. The actual 'insides' of the robot were unharmed, the robot could have gone in a whiteboard if we'd wanted to! So in that sense the armour was tough enough. Although the robot came out looking a lot worse for wear, the armour would have still held up even in that condition.

More info can be found here: http://teaminvade.co.uk/index_files/Page535.htm

Hope that helps