Way back when in the mists of time, 1 of the first guns I did a 'how to' on here was a sooooper noise suppressed SPR, It may well still be in the archives somewhere if you can be arse to find it, to it I fitted a suppressor and in it I fitted baffels and foam dampers like these.....
This is the original pic I posted on the subject, I now use a different method based on the same theme that is about 50% more effective again utilising ventilator fan foam filter and plastic card
Without getting into sound harmonics and how they work etc the key is to have low density foam (bigger bubbles), and to vary the size differnce between the baffels, make the hole going through the baffel a maximum of 10mm, also vary the size of the diameter of the foam hole in the opening between the baffels, if that makes any sense, or do the spikey thing as in my pic as this nearly achieves the same thing.
Most manufacturers provide foam that is way to small in diameter and to hard in density
I've made a fair few suppressors for various guns using 32mm and 40mm poly pipe, but don't try to make it to long as it does sag under its own weight, which can cause problems with bbs hitting the internal baffels if you dont get it right