With a water bottle—and, for the purposes of our analogy, a body—the density, and therefore the mass, of the water (
Ki) inside is largely inconsequential; whereas the volume, what exactly fills up the space inside, determines the condition of the bottle. Even if the
Ki inside of, say, Goku's body was
denser—even disregarding how little, if ever, the concept of
Ki densityhas been referenced—if the volume (or the
size, as inferred throughout the manga;
Ki becomes
bigger and
smaller, not heavier and lighter) of his
Ki was the same as when its density is "normal", his body would be largely unaffected. For example, when using the Kaio-ken, the density of his
Ki remains unchanged; instead, he directly multiplies the size of his
Ki, and because its volume approaches the limits of what his body has been trained to be capable of withstanding, every x-fold multiplier increases the risk of his body exploding from within, due to his
Ki becoming too large to contain.
However, God
Ki is not denser. For our purposes, the only confirmed unique properties of God
Ki is how much more refined the former is than normal
Ki; in fact, its "
clear, high quality" nature is why God
Ki can only be sensed by gods—at least in the manga. The only reason why Super Saiyan Blue's energy leaks from the body is because, again, Blue is simply overwhelmingly powerful; Goku
says as much, Gowasu
says as much, and Vegeta
says as much.
Being a normal Super Saiyan by itself "
overstresses" the body because they are drawing out dozens of times more of their
latent abilities than normal by drastically altering their physical shape—
transforming—which is a constant "
gigantic effort", resulting in their energy being continuously drained, regardless of whether they are using 100% of their full power or are even in combat; being a Super Saiyan God requires an additional transformation in order to unleash the absorbed powers of a god, further straining the body; and being a Super Saiyan Blue, naturally, combines the drawbacks of both, draining one's physical stamina more rapidly than before, which results in the energy their body can no longer sustain leaking through their aura.
In exchange for losing their power rapidly, their body is not broken from within by their energy. However, Perfected Blue, conversely, can utilize 100% of Blue's normal power continuously in exchange for physical health, risking self-destruction by trapping all of the form's energy within the body.