I spoke to a helmet guy about padding material: inside the bucket, and of course around the tubes where you might hit them in the car.
He was surprised that the roll bar and accessory manufacturers do not appear to use (or at least publish) any data on how much load compresses the padding by X amount, and even more surprised that I said use of sponge-appearing material (like water pipe insulation, you can compress it and it expands back) is common, and no definitive way to tell if it's useful at all in an impact; all it will do is prevent tearing injury to the impacted tissue, but almost no effect on reducing the blunt force. Eeekk...
If you read about helmet design, the interior only uses sponge-like material for comfort, and as an air seal and wind noise suppressant. The actual padding (protection from crushing and G force) is foam which is very stiff and only works once: if it's been compressed it's used up and at least the foam must be replaced (this presumes that the shell can be tested for integrity, otherwise the whole thing is a wall hangar).
Has anyone dented their roll bar padding? Did it stay depressed, or spring back? How much force was applied?

There is 2 different roll bar paddings... one for above
10.0 then the HARD stuff for 9.99 and lower... I have hit
my helmet on it but didnt hit hard enough to dent it...
the stuff for 10.0 and slower is the foam rap stuff(soft)

The soft stuff is absolutely worthless.

I've cracked Bell Helmets racing motocross back in the day, yeah that's a "s", I don't plan on doing at again, but the soft stuff will disappear when it's stuck between your helmet and a hard place.

The hard stuff, like I have in my car, doesn't seem like it'd do much on impact.

I have the hard(certed) padding in all my cars... to me
it seems like my helmet would just bounce off.. to me that
stuff is HARD

Take a sample of whatever padding suits your fancy, wrap it around a baseball bat. put your helmet on, and have your significant other give a what for on the helmet, and then decide which handles an impact best. I think it will be obvious.

I wish there were a durometer scale or similar for this stuff.
The helmet contents look pretty much like beach cooler material (I dropped one down the stairs once and very little happened), but how different is it?
Is the stiffer padding split in half (not slit, since it's not flexible) to go around the tube, and fastened with clamps?
I'm considering having a 6 point installed in my street-only car, and I would certainly use nothing but the stiff material; unless you're really restrained in a roll-over your scapula, tibia, radius, ulna etc. may strike a tube while flailing around; the bone is at risk.
I'm going to see if Snell and TÜV have any info on-line.
Any links or references appreciated!

I am wondering about its flame resistance and toxic smoke if it burns...