I'm not 100% but it might be called PVC or Plastic clear A4 sheet xxx Micron in the US, good luck!

Perhaps something like this:

https://www.amazon.com/QBIX-Mylar-Stencil-Sheets-Transparent/dp/B07K31VXVG/

Though some of the reviews seem to suggest that seller didn't send the highest quality items to some customers.