Linen postcards are easily identifiable by the type of high rag card stock they were printed on which was produced with a linen finish; a textured pattern distinguished by parallel and intersecting lines resembling linen cloth. The face of the card was the textured side and the reverse was smooth just like other postcards.
Due to the use of this paper, linen postcards could be printed with brighter inks creating brightly coloured images, making them a huge advancement over the earlier white border postcards. Linen postcards' heyday was from the 1930's when they were introduced to about 1945.
I have quite a collection of these linen postcards mainly featuring town views, ‘important’ buildings, and factories. I believe they are mainly heavily retouched black and white photographs, rendered in vibrant colours. This retouching gives then a unique look.