Surfing Waves

I was told by a waterskier that rash vest reduce heat under a wetsuit? Any truth?

it reduces heatloss, not heat

I know you get thermal ones which keep you toasty but this guy claimed that a standard rash vest stops the wetsuit working as well as the neoprene isn't against the skin.

yeah it's true, someone's probably got the technical bull on here but yeah it lowers the perfomance of the wetsuit.
bodyheat warms the water between the body and wetsuit plus the water in the neoprene, rash vests stop this from working so well, something like that anyway

Yes it yields a cooling effect - I never wear a rash vest under a wetsuit in this country (UK – year round surfing).

I rely only on wetsuit ability.