4x8 deck material

I need some advice.

I’m essentially turning my flat bed router into a “pod and rail” machine by cutting 12, 5" wide “tracks” across the width of my supplemental deck then placing 5" x 5" Vac pods in the tracks that can be adjusted across X.

I’m not happy with the vac loss with my current configuration and would like to replace the actual grid deck with another in the design above. The question is - what’s the best (OEM) deck material and where can I get a 4 x 8 or 5 x 10 sheet of this stuff? I"m thinking super hard rubber or some sort of closed cell plastic/vinly. My primary machine uses hard rubber and my other machine has a hard plastic deck. The cellular PVC I used for the supplemental deck doesn’t get it. It must be open cell because with all ports plugged on my prime deck I get 23.5 but when I apply the PVC deck and plug it I get 17.5, even after painting it.