Here’s an interesting piece of research you may wish to share with your class
On the Effectiveness of Aluminium Foil Helmets: An Empirical Study
There’s an accompanying website here too!
This work was done back in 2005 so after reading the information on the website and the published research you could challenge your class to do their own modern investigations.
Once they have designed their helmet they could test whether wearing the helmet has an effect on mobile phone or wifi signals, or if they get a better quality Skype call. Maybe a Facebook status written wearing the hat will get less likes than one written without it!? They could use Glogster to report their findings.
Of course the hat has no real influence on the experiments but it is a fun way to teach about variables, controls and how to conduct research.