Is there a chemist out there ?
 

What are the chemicals needed to make our own filler foam ?
A metre of foam then a metre of sand then a metre of foam then a metre of sand then etc etc. in the firehose,,,,,,,what do you think?

could use tins of house filler foam that expands pretty good or get a load of bean bag polystyrene pallets

How carcinogenic do you want it to be?

I can think of several methods but most would give you cancer just by looking at them......