Hi, it does look like some sort of filter and when pick it up and you rub it with your fingers it disinter grates…It could be bits of insulation blowing in from somewhere. Possibly as wind blows through the floor drop vents it's blowing bits in from underneath the settees? What sort of material is it?
Thank you.By looking at it does look like bits of polystrene i would investigate in your caravan you might find some more good luck