So yeah, colleague was in the pub with mates and apparently they came up with this "great idea" for an inflatable cycle helmet so you could just fold it up and put it in your bag when you get somewhere.

I pointed out that this was a terrible idea as it would just burst upon impact. She rolled her eyes and said obviously it would be made out of a robust un-burstable material.

So I said that her idea was basically to invent an incredible new material that was both flexible enough to fold into the a tenth of it's inflated size and sturdy enough to remain firm after a 40mph impact. She said yeah with a completely straight face.