Over the years I found unbleached Calico, which comes in widths upto about 72", which is good for skinning flats {Backdrops} & far cheaper than canvas. However it needs to be unbleached because it will shrink & tighten upon the frame. Also a good clue is to spray both side with water while on the frame & allow it to dry & shrink on the flat frame before sizing {If Poster water paint is used]. However if it tends to sag after drying, you could just wet it again on both sides using a spray water bottle [Hudson Sprayer]

If you know a friendly Upholsters &/or furniture manufacturers, they buy the unbleached calico for underneath chairs, which comes in bales, that are made up from off cuts & end of loom runs from India. Usually it's only a few dollars a metre or at least a few comps. Which also is handy for use in the Wardobe & knocking up costumes ect,.

Over the years I found unbleached Calico, which comes in widths upto about 72", which is good for skinning flats {Backdrops} & far cheaper than canvas. However it needs to be unbleached because it will shrink & tighten upon the frame. Also a good clue is to spray both side with water while on the frame & allow it to dry & shrink on the flat frame before sizing {If Poster water paint is used]. However if it tends to sag after drying, you could just wet it again on both sides using a spray water bottle [Hudson Sprayer]

If you know a friendly Upholsters &/or furniture manufacturers, they buy the unbleached calico for underneath chairs, which comes in bales, that are made up from off cuts & end of loom runs from India. Usually it's only a few dollars a metre or at least a few comps. Which also is handy for use in the Wardobe & knocking up costumes ect,.

Others like Timbo may have other & better ideas!