I think you might find the following observations useful. If your results differ from mine, please comment in this thread.
I have had the pleasure to do density testing on Alumilite White, 610 foam, and Super Foam 320. Frankly, I have probably done too much, and got far too deep into it. After all, the alternative, wood, is not as consistent as any of these, so the results I will be offering soon are going to be far more reproducible then any wood product. Still, I offer these results for your consideration and possible use.
My first tests were done on Alumilite White. This product can be mixed either with equal volumes of Part A and Part B, or by equal weights of Part A and Part B. My test shows that both create perfect results; strong, consistent, excellent.
I did notice that Part B is slightly heavier (denser) per unit volume then Part A. What this means is that if you measure by weight, and not volume, you will end up with a little of Part B left over at the end of the bottle.
I also noticed that this means that if you test the density of the two mixes, the equal volume mix is slightly denser then the equal weight mix. The difference is so little that it is hardly worth mentioning, but some of us are working on suspending baits so you should be consistent in which method you use. Also, the measuring cups that are disposable are not marked with as small a unit as you can get if you use weight, so, in short, I suggest that for greater reproducibility, the use of a scale is best. A scale that measures down to 0.1 grams works well. Keep in mind that most of us really don’t need that kind of accuracy and the plastic works well either way.
I also noticed an additional factor. For my testing, I used a 5/8” diameter wood dowel to make a mold. I made the mold 4” tall. The reason is that as we mix the two parts together, we introduce bubbles. These bubbles do not have time to escape before the plastic sets up, but they do rise, so the density of the plastic at the bottom of the mold proved slightly greater than the plastic at the top of the mold.
OK, we are talking differences, so now I need to give the differences. With equal parts, by volume, of part A and part B, with no micro balloons, you get no expansion of the plastic as it cures, and the density of the bottom half is 1.09 grams/cubic centimeter. The density of the top half is 1.08 g/cc.
If we mix equal volumes of Part A and part B, with no micro balloons, by weight this time, the density at the bottom is 1.08 g/cc and the density at the top is 1.07 g/cc. Again, you get no expansion.
With so little difference, you might as well consider there to be no difference, but all of my test will now use equal parts, by weight, for the test. Notice that with no micro balloons, the density of Alumilite White is 7% greater than water, without hooks, eyes, hangers, etc.
OK, enough for now, I continue with Alumilite White using Micro Balloons next.