What thickness Lexan to keep LH2 out?

I'll be building my robot for the champs next week and have been drawn up against LH2 in qualifiers :cry: . How should I keep him out of my robot? I was thinking 10mm or 12mm lexan from here:

http://www.ebay.co.uk/itm/Clear-Polycar ... 4abbbdc80f

Any thoughts / suggestions?

Cheers

Dan

6mm should happily do the job.

Eag I would have thought 6 mm should do, depending on the mounts, make sure it can flex, if its to ridged it could crack.