The interior fabric used by Scamp
in their trailers since the late 90's is a waterproof marine headliner material.
It looks like and has a consistency like you might imagine Rats have on the outside.
first lines the interior with a Reflectix insulation which is a foil backed insulation product that is very thin yet still provides some R-Value as an insulation and then they cover that with the "Rat Fur".
It had some interesting properties too.
Velcro will stick to it very well but the velcro can also pull the fur from the insulation if not careful.
The Rat Fur also provides some degree of sound absorbtion and also makes the trailers very cozy and warm feeling.....to me at least.
It is waterproof enough that Scamp leaves it unprotected as part of the bathroom interiors and they claim it will not mildew either.
Before this Scamp and several other manufacturers used a material called Ensolite which is a rubbery insulation with a rubber skin.
This looks sort of like Elephant hide.
Both of my Trillium's had this inside and it was not too bad. Some insulation and some sound deadening too.
uses a Kanga backed carpet which is just Carpet with rubber backing. They used to use some fairly crazy sculpted shags before this.
Hope this helps.