Best Coroplast thickness for a small car undertray?
 

What's the consensus view?

Useful for mockups and testing, not the long haul. If you do use it here's a[n untested] suggestion for shaping and edging it with wire reinforcement.

https://ecomodder.com/forum/member-f...12-1-55-49.png

Shallow notch for taped edge, deeper to wrap the edge, Wires through the corrugations to hold curved shapes.

And: stiffer along corrugations, bendier with corrugations 90 degrees to bending force. freebeards post shows the need for reinforcing in the bendier mode

So, how thick should the Coroplast be for stiffness in an undertray?

4mm? 6mm? 8mm? 100mm? What?

I think the deciding factor here is what DF is likely to be created. In racing it is the goal, and not a full negative result (pun intended) here I suspect combined with how the panel is supported and what the mounting spans/frequency is, and what effect any ambient heat (exhaust, etc) will have on the panel to weaken it.
Some flexibility might be a plus in helping have a favorable outcome with the occasional road debris.
My application I'm seeking DF first then drag reduction, I'm leaning towards 8mm CF/kelvar honeycomb custom fitted/shaped w/HT epoxy.

Whatever is free, it's only for mockups.

Maybe for complex shapes like a diffusser. For flats or simple curves, Polymetal/Alumapanel composite.

FWIW I have been using a free used political sign for my belly pan for over a decade. It measures 3/16" or 5mm. it is more reinforced than the photos in my album show but other than that is is holding up fine. My car is a diesel so the exhaust is fairly cool. I covered the whole bottom of the car from just behind the catalytic converter.

200mm. itll keep all air from going under the car

' consensus '
 

Years ago, I thought it was generally agreed that, the 10mm Coroplast, from The Home Depot had turned out to be more than adequate for belly pans.
It's a thermoplastic, and will 'yield' at some temperature threshold, but exhaust components can be insulated, or heat-shields fabricated to mitigate heat effects.
Sag testing will reveal necessary center-to-center support spacing.
And hat-section stiffeners can be attached wherever deemed beneficial.
Consider 'sections' of pan, which can readily be removed for inspection.