Solar-Flattening Fiskars Cutting Mats

Fiskars cutting mats must lie flat on the table to be of any use, but they’re remarkably sensitive to warping due to localized temperature variations; a hot cup of tea can wreak a remarkable amount of damage. Suggestions from the InterWebs generally involve a clothes iron, temperature tweaks, overnight cooling, and unpredictable results.

Given that the mats are large polypropylene sheets, I figured applying moderate heat to the entire mat while it’s compressed between two flat plates would work better:

That’s one of Mary’s 36×24 mats atop an MDF sheet (with pictures of wood laminated to both sides), under a 7/32 inch = 5.6 mm sheet of non-tempered glass, with a maple shelf supporting the last two inches of the unwarped edge, all sitting on the driveway in full sun.

The first attempt started too late in the afternoon for good heating and, after a few hours, had only slightly reduced the warp. Laying it out the next morning got the mat up to about 110 °F = 43 °C around noon and the warp was completely gone by evening.

I don’t trust the IR thermometer’s temperature measurements on glass, but the surrounding MDF and driveway were plenty hot.

The next sunny day flattened the warp out of 24×18 inch mat on my desk, so success wasn’t a fluke.

We noticed that the larger mat is now uniformly smaller by about 3/16 inch along the 36 inch width and 1/4 inch over the 24 inch height. It was a tag sale find with unknown provenance and, due to the warp, Mary had been using her other large mat for layout, so we don’t know if this one arrived a little short or if my technique both flattened and shrank it.

The smaller mat seems unaffected by its similar treatment, so your mileage may vary.

In any event, a flat mat is much more useful than a warped mat, so we’ll call the operation a success.