if you are going to use them, make them yourself. I have a sewing machine, and buy the fabric by the meter. I have made them with 4 different materials, and 2 thicknesses on two of the materials. ( I think it is called felt, but, honestly I don’t know) I wished you lived in Mexico I would send you a bunch for free just to get rid of them. I have them in black, grey and white. never understood why they don’t make em white more often.
(a postive note is that you can go a size or two smaller than a plastic pot without effecting yeild.)