@juul, note that glycerine is denser then water. A solution of 95% glycerine and 5% water at around 5 degC is about 1.25 g/mL, so by volume it would closer to 3/4 of the capacity.
I hadn't thought about that. Good point.
Of course water won't go through a phase change above 0 degC, so all told the glycerine might prove to be a better temperature buffer if you can get it to actually freeze.
It definitely still will be. The amount of energy absorbed during thawing is still around 150 J/ml vs. the ~4.2 J/ml needed to raise the temperature of water a single degree.