it's part marketing and part science
The foam density is not in fact a weight but a measurement of mass per unit of volume and it is measured in kilograms per cubic meter (kg/m3)
Basically, the higher the density of foam, the greater level of impact resistance.
The impact resistance is the ability to push back against weight and prevent the foam from ...
In my opinion to improve your jiu jitsu you need to train more jiu jitsu.
I can se just a few cases in which I think that a parallel train could be indicated for beginners in order to drsticaly improve its game.
If you are a sedentary person, overweight or underweight person. The train should be focused on strengthening, in order to avoid injuries.