I have done some research into it previously by looking at using carbon fibre or fibreglass apex shaped canes to lighten the pads and give the structural strength still.
Air in another option we have looked at using but would require some RND investment to get samples up and running.
The "canes" in a set of pads I cut open were a piece of folded cardboard to form the apex and some garden cane cut to the same shape so not very technologically advanced considering the model of pad and price tag!
Everyone seems to band aboUt d3o on here but probably haven't seen it in sheet format to realise just how heavy it is let alone the expense of it.
With the Air in the pads - I would see that as smaller versions of the "clappers" you get at sporting events - the issue would be getting them housed in an appropriate material and how to counter the loss of air over time (like tyres) would you have some form of pump?
The other option might be some form of "gel" filling for the tube rather than air - similar to what is used in shoes perhaps?
cardboard in pads - humm good job you didn't put them in the bath
!!