I weighed a 15-yard bolt of the 60x60 and it was 5 lbs. 7 oz.
The 75x75 weighed in at 4 lbs. 2 oz.
Considering that the cardboard is also included in that... there is at least 25% less material by weight in the 75x75. I asked if the different fabric was chosen as a cost-saving measure and that's when I was told that the 75x75 actually costs the maker more.