The good stuff is 8-ply rag/alphacellulose board -- or several layers of white rag/alpha matboard wetmounted together in the vacuum press. Trim to frame size, and cut a "mat" out of it -- stretch the needlework on the fallout, then put it back in. Lacing is done with 100% cotton thread.
Most customers are not willing to spring for preservation framing for their hobby cross stitching works. So, we try to offer a good half-way method. That is, we use nickel-plated brass straight pins (no rust/corrosion) and ArtCare foam center board. As above, we cut mat from frame-sized board; pin to the fallout & put it back in.
It's not maximum preservation, but it's good for a long time. In any case, it's worlds better than the corrugated cardboard & masking tape the cross stitchers would do on the kitchen table.
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Jim Miller, CPFcm; GAFP Committee Member