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?