flexible expanding foam

[rogerthebodger]

So you would fill it with harmful chemicals which (whether you like it or not) WILL end up being discarded in landfill one day
That was the point of my post. Not one of removing rubbish from our oceans- a move with which, I heartily agree

Remember that a fender is intended to squish when compressed, hence the low psi. Filing it with stuff will prevent it from doing this. You don't want hard fenders.

I was talking about filling a fender with flexible expanding foam may be neoprene as used in rubber sealing strip like foam draft excluder strip and foam backed PVC covering.

If that is " harmful chemicals " my little bit will not cause too much harm,

Being flexible foam it will not make the fender too hard, depending on the foam density.

 

[ganter]

For a small fender use an old bicycle inner tube for a larger species use an old car inner tube.
Make a slit in the fender just large enough to insert the tube with the valve accessible. Inflate, stuff the valve in to the fender and repair the slit with heat from a soldering iron.