I just weighed my Ultimate Lubix GuHong and LunHui. The GuHong came in at 90 grams. and the LunHui came in at 100 grams. Now, obviously these are lubed... so that probably adds something.
The stated weight for the two types of GuHong's (POM and ABS), the LingYun, the LunHui, and the Zhanchi on WitEden is:
"GuHong
Size: 5.7cm
Cube Weight: about 80g
Material: ABS
POM GuHong
Size: 5.65cm
Cube Weight: about 100g (ABS GuHong about 80g )
Material

OM (not ABS)
LingYun
Size: 5.6cm
Cube Weight: about 87g
LunHui
Size: 5.6cm
Cube Weight: about 95g
Material:ABS
ZhanChi official version
Size: 5.6cm
Cube Weight : about 85g"
So lets calculate the density of each... Density=mass/volume
GuHong 0.43198 grams per cubic cm
POM GuHong 0.55444 grams per cubic cm
LingYun 0.49540 grams per cubic cm
LunHui 0.54095 grams per cubic cm
ZhanChi 0.48401 grams per cubic cm
That pretty much sums it all up (assuming all weights and sizes are valid... I would question some of them).
-achilles308