The material could be a bit more dense. This is quite like the 4 cm version, but of course blocks a little bit more. In my specific use case this is also a bit easier to install in most cases. Out of the box, these absorbers have a bit of a nasty smell to them, but that will go away in a day or two. I think the 4 cm version is a bit more cost effective, but otherwise this is very much recommendable.