Insulating WC cistern

I am having problems with condensation build-up on the outisde of my porcelain w.c cistern, due to the fill being sourecd directly from the main cold water supply. I read a reply on an older board suggesting insulating the inside of the cistern with foam. Any ideas of what kind of foam (and glue if necassary) that I should use? Thanks.

If the water is really cold, insulation may not stop the condensation. Insulation only slows the transferance of heat, not stops it. Just a trivia thing, there is no such thing as cold, it is the absence of heat. Heat moves from warmer to colder areas, always trying to even things out. INsulation slows that transfer.

It may be better to bite the bullet and buy a mixing valve and run a little hot water to the fill to temper the input. My unprofessional opinion.

Most insulated tanks have styrofoam.
I don't think it needs to be very thick to work.
Glue? I would only be guessing.

First thing to check though, would be the flapper.
If the flapper is leaking, you will certainly have a sweating tank.