What would you class as a acceptable thickness for a carbon panel to fit the underside of my car ?

I believe it's 300gsm 4x4 twill, something around .3mm i think he said doesn't mean much to me though.

The chassis has many points to attach it too and is dead flat from behind the engine to the back where the link boxes end.

Depending on the thickness we go for I may have enough spare to make up a undertray for the engine which would be handy so I'd like to make the most of it if I can.

Any advice would be appreciated