Doing a little bit of research online turns up that 'vlies' is German for fleece and Plano is from the Latin 'Planus' for "flat" so "vlies planos" is flat fleece.
Never heard of it. Fleece is supposed to be made from sheep's wool. As we have sheep on the farm I can assure you their wool is nothing like what these sails, rugs, etc are made with.
So, by searching I found this:
http://www.alibaba.com/showroom/flat-fleece-fabric.htmlSo, flat fleece fabric is what it would known as in English. Most assuredly of the polyester kind.
Since you can specify certain weights when you order I am sure you really need to run to a fabric store of some repute to sample their wares.