I've had to ship lots of things overseas through the years, and I've yet to ship anything whos weight and volume matched the carriers volumetric weight calculations. The items I've shipped have either been much heavier than their volumetric size, or much larger than their volumetric weight.
Today, for example, I've shipped some old cockpit panels from a 737. The package weighed just 2kg, but was 95x30x50cm in size, so I paid for a volumetric weight of 24kg.
So, I'm wondering what single material, generally, would create a volumetric weight of 1:1? I thought this might be water, which weights 1g per cubic centimeter, so 1kg of water would take up 10x10x10cm, but this equates to 0.5kg in volumetric weight... so I have no clue.