Simon - Warner Bros. made linen lobby card sets, inserts and 22x28's for a couple of years. I guess the idea behind using this kind of stock was because the posters had a pebbled finish and looked much nicer and more special than the lobby cards and posters printed on normal flat stock. And as Starling mentioned, they brown badly with age, turning what was probably off white paper stock sepia brown. Folded linen inserts and 22x28's can really take a beating and will sustain a lot of damage. The fold lines on linen posters are the worst; the finish can chip off and show the under layer of paper. The lobby cards can look nice, but have to be handled carefully because they can chip, scuff, tear and start to look bad without much effort.