Dave,
I don't know if is of any help to suggest that this material may be a grade of Presspahn. (
https://www.presspahn.com/product-so...ial-solutions/ ). It might be worth a look at their web-site to see if any information there is useful to you.
Do you think that steam (actually mist in scientific terms) from a kettle or similar would soften the sheet to allow it to be flattened by clamping?
PMM