Polystyrene bar/tubing for cores

Hi all, new member here and I’m looking for some help. Based in the UK but what I’m after is polystyrene or equivalent that can be rotted out from inside a carbon tube. Ideally if I can buy polystyrene bars or tubing already turned down that would be ideal, can someone please help?!?!

Find a foam supplier, many of them have wire cutting equipment and could cut your cores to your size.

Thank you very much.