I could easily wrap a pipe in foam but I see where creating the air space could be challenging. I will think about this some.
The foam would have to be a foam rubber tough enough and dense enough to avoid the chickens 'crack like' habit of pecking and eating foam...
Then you have chickens eating paint chips which is not real great (for them or you)
Modern latex/acrylic paints are for all intents inert once dried and cured...
But, I would leave them plain wood anyway, they well get a nice ground in poop light gray/brown look to them soon enough...