Side panel material

Our Devon 2008 has grp rear and roof but what are the side walls .They look dull compared to the grp almost like white faced boards.
Nothing wrong just curious when polishing today.

The sides are Styrofoam panels.

https://www.practicalmotorhome.com/advice/motorhome-construction-guide

Years ago I bought a gallon (probably 5 ltr) can of Autoglym renovating polish and a machine polisher. The machine is quite expensive, from Machine Mart but you do need a powerful one, not these namby pamby buffers you sometimes see. If you use a slightly abrasive polish specified for the job and use this method, the end result is better than new. You can slide your hand over the bodywork and it is as smooth as melting ice. Once a year is good enough to keep it looking pristine, and rain and other water just runs off it faster than an escapee from Dartmoor.