Best products for baffle material s ?

I've seen a few concrete enclosures. My thinking has been that the Styrofoam will significantly lighten the concrete while not losing anything in strength. Then I think of stacking different materials... one dampens the next, dampens the next etc...
I believe that the epoxy will be another dampening material and equally strong, the enclosure should be very dense and as well damped as any material out there.
No testing, nothing scientific about it, just a hunch that I'll have to try someday.

Hello PBNaudio, your input much appreciated. I'm just getting back to this project for 'the perfect cabinet" for the B&W drivers presently in the synthetic cabinets of the B&W Concept 90 CM1s (which vibrate 'nicely' with very little energy input ;-) .
I now have someone who is happy to do the cabinet work as an interesting joint project and has the necessary woodworking tools and skills; as he would like to make speakers for himself from a kit. I enjoy music through the CM1's (with 25 lbs of lead on them) so have time to do what I want. I like to think there may be a better way to provide 'breathing room" behind the cones than simply using a conical opening-which I appreciate as practical- so I want to evaluate more complex ideas. Any suggestions for something more 'extreme'? I'm not the least concerned with diminishing returns-simply going all out--without wild expense. What do you think of a "variably" slotted opening instead of straight cone?

Hello S7horton. I've been on hold with this (I think my massive "myocardial infarction" had something to do with that :-) ).
Ready to get back to it now. Looking to go all out for the construction of these little cabinets. I'm considering all aspects of interior cabinet design-to kill standing waves & resonance. I'll be in touch thanks.

Is there a benefit to adding surface area to a speaker?

Chobham