“a good bass trap has a lot to do with density”, well it’s not that simple… The performance of a bass trap relies on several parameters, the most important being:
- Air flow resistivity
- Air gap behind the bass trap
- Its placement in the room (room modes are highly localized)
- Backing material and fabric (or whatever) material used to cover it
The density itself actually has little to do with the bass trap performance. The resistivity is the key parameter, but there is no one simple rule like “the higher the better”… There is, however an ideal resistivity for a given bass trap and you can calculate it with this fantastic website: http://www.acousticmodelling.com/porous.php
If you play around with the values, you will see that for thin panels a high resistivity is better, but for thick panels the trend is reversed.
It’s hard to tell if these foam panels would be any good without knowing their flow resistivity. Maybe you can contact the manufacturer and ask if they have tested them for resistivity and can give you the value? However, if this material is cheap I think it’s safe to assume that it is not as good as the material bass trap are usually filled with, which to my knowledge is mostly glass or mineral wool.