Hi everyone

I am facing a constant issue with the top sacrifice board, as it loses planarity over time. I work on thin sheets (1.2mm) and a 0.03mm tollerance on the table (1500*1500mm) is critical to obtain quality finish products. Actually this planarity issue is the source of the most failed finish products I make.
I am using now an expanded PVC board, German quality, but it takes only several days (less than a week) to loose the planarity. My guess is that moist is the actual sourse of the problem.
I do often surfacing jobs, but not very efficient. Therefore I am lookuing into alternatives that are more stable over time.
Harder/denser plastic bords would be interesting but after surfacing the surface is quite slippery and vacuum cannot hold the parts in place in a reliable manner.
One other thing I would like to consider is rubber sheet that can be machined. I saw smth like this years ago on a French made Mecanumeric router. I remember it as quite resilient, high friction, and probably more stable over time.

If anyone has recommendations for this, help is appreciated.

Thanks a lot
Marius