For the perforated pipe inside the silencer is one with many very small holes going to quieten the sound better than one with less bigger holes.
I cant seem to find any useful info online.
in my experience the perforated tube does silence better than the louvered ones *when packed correctly*. also, the louvered ones create a boundary later that reduces effective diameter. :twocents:
I guess it is not only hole size that matters, but also the proportion of holes vs material. Perforated sheetmetal comes in different percentages, i.e how much of the total area is holes