I have used grosflex in a shower and partially along a wall, dont know about heat retention but it is definetly warmer to the touch than tiles. It is quite easy to damage it though, hasnt been a problem in the shower but on the wall if you banged into it with anything then you can easily dent it or break it. The shiny version of it looks a bit cheap on the walls in my opinion even though that is what I have as I wanted the plainest type, kind of grey marble effect. The matt ones are nicer but limited range. In a small shower it is great cos if you touch off the walls accidentally its not freezing like tiles.