Yes steel accounts for the weight. I was wondering though, once the case is has all your components in it, just how heavy it is? Can one reasonably fit person lift it OK, or is it so heavy it is best not to try?
Mass damping of side panels likely makes about kilogram.
Steel's 2½ time the density takes care of rest.
As for components those likely make about 5kg with PSU being about 2kg.
Motherboard, CPU cooler and HDD easily makes couple kilograms, higher end graphics cards are again likely in class of 1kg
And if that OCZ PSU is say five years old would be for replacing it soon, it has cheap capacitors badly placed for cooling.
Instead of second tier Teapos can be even worser ones like TRec's in this individual:
https://www.pcper.com/reviews/Cases...tream-Pro-600W-Power-Supply-Review/Under-Hood
Before current Lian Li PC-A71B had couple full towers from steel.
Chieftec DA-01 likely had about 15kg empty weight and previous owner had added bitumen mat for mass damping so it certainly weighted 2kg more.
Coolermaster Stacker STC-T01 had 14,7kg weight and that was already with Aluminum side panels. (added BeQuiet's combination mat to panels)
After very thorough lining with BeQuiet's combination mat Lian Li is likely still 5kg lighter than those.
Anyway 20kg of Nanoxia Deep Silence 6 makes Define's weight light...
http://nanoxia-world.com/en/product...-silence-6-rev.-b-anthracite?c=127#block-tech