No mate... Once cured, it's air tight and waterptoof.... Like a waterptoof honeycomb (if applied correctly) ...... To be fare I bought the cheapest one, I'm sure there are prob better quality versions with better expansion... It's used a lot in the window fitting trade to seal gaps when fitting..... So it's basically weatherproof... the bubbles are tiny and it would only be any broken bubbles on the surface of the foam that could hold a little bit of moisture.
It needs a little thought, as once a can is opened and used, you really need to use it all at once, it sticks to anything and the nozzle will block up , as this too, will start to cure, there are cleaning agents sold separately to unblock the nozzle, but that's just more expense..... A decent sized can of the foam is around £5, and it did the 16mtres with a bit of waste...... I'm gonna mess about with the spare lengths over the weekend and another can of foam, try and work out a way of totally filling them.......
There is a case to say that the foam may not have fully cured inside the poles I did, as I was a bit hasty to test it and only left it for 18hrs and not the 48 that I intended...... I think it's known as "learning on the job" lol