How to install additional sound deadening material inside your Howard Leight Impact Sport muffs (disassembly starts @ 1:52). *READ DESCRIPTION FOR FOAM INFO*

I used closed cell foam pieces to fill in dead spaces inside the muffs to improve the noise reduction of my Howard Leight shooting muffs. The foam is just a scrap from a yoga mat I got at Walmart. It is similar to thick craft foam or foam puzzle mat material.

Unfortunately, I don't own a decibel meter, so I can't give a specific number of reduction, but it did help.