Was curious about this, so I've just done an experiment.
Stack 1: 20 original DVDs (the most I could find in the house)
Stack 2: 20 original CDs
Stack 3: 20 Datawrite printable DVD-R 8x (Ritek G05)
Stack 4: 20 Datawrite orange-bottom CDR
The 20 DVDs are approx. 1 disc thicker than the 20 CDs (the top disc can slide over onto the CD stack)
The 20 CDs are approx. 0.25 disc thicker than the 20 DVD-Rs
The 20 DVD-Rs are approx. 0.5 disc thicker than the 20 CDRs
The 20 CDs are approx 0.75 disc thicker than the 20 CDRs
So the thickest-hubbed discs are DVDs, then CDs, then DVD-Rs, then CDRs.
BUT... that's not the whole story as the centre (hub) of the disc is thicker than the rest. Next experiment: press down on the edge of the stack, so I'm comparing the data areas instead:-
The 20 DVDs are approx. 0.5 disc thicker than the 20 CDs (top disc can no longer slide)
The 20 DVDs are approx. 0.25 disc THINNER than the 20 DVD-Rs
The 20 CDs are approx. 0.75 disc thicker than the 20 CDRs
The 20 DVD-Rs are approx. 1.5 disc thicker than the 20 CDRs (top disc can slide over)
So the discs with the thickest data area are DVD-Rs, then DVDs, then CDs, then CDRs.