Brands and Performance:Different internal designs provide different results. Some brands offer several designs and most brands offer at least variations within a design. So here's some that have been mentioned.
Flowmaster Uses internal baffles. The versions that are usually discussed are have V or "delta" shaped baffles.
The gas has room to expand immediately upon entry. These are offered in several series, some (10, 40) are louder than others (50, 70). They also offer several other internally baffled muffler designs.
Summary of offerings DynomaxIn recent years has added several mufflers using different designs. But they started with "turbo" mufflers
"turbos" use internal tubes running through center chamber and reverse the direction of the flow a couple of times. The name "turbo" comes from one of the earliest applications of this design - turbocharged Corvairs. When Vizzard first tested mufflers for flow a few decades ago, several company's models (Not just Dynomax superturbo) did very well.
Ultra Flow mufflers are a straight through perforated pipe with insulation packed around them. In design cncept, they are very similar to
Magnaflowwhich also uses a straight through design with insulation.
I suspect the heritage of these designs are the 'Glasspacks. I don't believe the insulation on any of these designs 'blows out'. It seems more likely that it can get moved around a bit and/or compressed a little during initial use.
For the record, Magnaflow also makes a chambered muffler series (XL) and a Glasspack series.
Accurate LtdThey have had a few different mufflers including some designs based on the stock originals. Here's one from around 2001 for an a-body that someone cut open.
Older Stock Based Muffler design (or see attachment) and a newer performance design (click on link for cutaway)
aCM-912These photos are both from a long
thread on muffler flow/restriction on FABO.