Your choice of the most "inert" cabinets ?

I agree with bdp24 the best cabinet is none, others can include Bent and Formed Laminations, I have seen fabricated steel used, Celestion used Aerolam , an aluminium honeycombed laminated material. Cast concrete is fun and not to mention an easy favourite , Lead Lined . The sand filled cavity has been used in the UK for transmission line cabinets for years, I love this hobby, all roads can lead to Rome.

MDF is good and practical. Not sure that there is a best. Amusing to see proponents of inert cabinets also supportive of rigid metallic or ceramic drivers. Gee gosh golly - speaker cabinets need to be inert but I guess it is ok for the diaphragms on the drivers to ring like a bell? Slight disconnect or what...

Hmmm, cast concrete sounds intriguing. Wondering why no one is using this approach. Obviously weight is not as much of a concern seeing loudspeakers already out there weighing hundreds of pounds...

The best I have heard move and breathe like an instrument. Harbeth and Audio Note come to mind. 

Those of us who've been in this hobby long enough know that 'resonance' is not a bad word when it to comes to speakers. Am listening to Govt Mule Live now, and my Spendor's resonances sound good as %$#&.