the spray foam is gonna get hard after you spray it and then when it is
compressed by the expansion of the joint it will be crushed and not go
back to its original position... the original stuff is tar impregnated
felt and seems to work OK until after it dries up.. how about a pressure
treated board with tar on it?????

The whole point of the expansion joint filler is to allow the concrete to expand
and contract and to maintain a water resistant seal so the soil is protected
from losing its bearing capacity. Putting a rigid piece of wood in place of the
felt would either cause the wood to be crushed or the concrete to spall under
the pressure. Stick with elastic material designed for the task.

Regards,

John