The bedspread is edged with a double thickness of black fabric. My plan is to unpick the stitching of this edging at each end of one side, so that I can slide a length of 15mm copper pipe* through it. Then I plan to support the copper pipe at each end with curtain pole brackets. (I had thought of using curtain pole instead of copper pipe, but the narrowest available seems to be 28mm, and I think that would be too fat to slide into the bedspread edging strip).
But the bedspread is rather heavy (it's backed with panels of black corduroy and velvet), and I am concerned the pipe will sag in the middle. What can I do to stiffen it? I had thought of filling it with cement, but IIRC cement corrodes copper over time. Another thought was to fill it with loose sand and vibrate it to compact the sand really well, but I'm not sure that would make the pipe rigid enough; yet a third thought was to fill it with expanding foam, but again, would that be effective?
Any other suggestions? The bedspread is 1.65m sq. Picture here https://ibb.co/kZwK2f (in reality, the colours are richer than in the picture).
*it's a length I have spare, but I could get some 22mm pipe if it would be better.