The mat surface is a hard surface in a metal tray with the wrist support around it.
You flip the mat within the tray to obtain different resolutions for your mouse to pick up on... or just when one side gets dirty and you want the cleaner side before you throw it in the dishwasher.
One of these maybe: https://www.razer.com/gb-en/gaming-mouse-mats/razer-vespula-v2
I assume dual-surface means you can detach the wrist pad and flip it over?