With this membrane sanding is an experience in itself. SIA was the first manufacturer to put this form of barns on the market and still makes the best fleece. SIA membrane is a kind of wool blanket that adapts easily to the contours of the object to be sanded. It was initially made for the automotive industry but soon other parties also discovered the convenience and durability of this way of sanding. I use it a lot in finishing my products. After mechanical sanding until grain 320 I go, after the first layer of oil has hardened, further with the SIA Very Fine (red) after which it is oiled again. If this layer is hardened there is Sia nonwoven Ultra fine (grey), followed by a low oil and and finally there is sanded (polished) with Sia Micro fine (gold). Very Fine (red) is similar to grain 320 Ultra fine (grey) is similar to grain 600 microfine (yellow) is similar to grain 1000 Tip: Do not order more than you use in 2 years. Because the membrane, if it is not kept under the good conditions, after about 3 years goes backwards in firmness and strength. Delivery Size: SIA Fleece Package comes: 1 strip of 10 x 100 cm. SIA membrane Very fine. (is similar to grain 320) 1 strip of 10 x 100 cm. SIA nonwoven Ultra Fine. (is similar to grain 600) 5 Skins SIA Micro Fine (is similar to grain 1000) of 115x152mm.