Shame that everyone poopoo'd your idea, but you are not wrong for asking. To be fair the technique is still widely used on race cars with temporary sound restrictions.
A company called burns stainless offers this solution in various sizes. Most tubi exhaust now usually use stainless wool or scrubs over glassmat, but you can still use glassmat as it is slightly cheaper but wears out quicker. For long term use, you should go with steel scrub.
Burns stainless offers both in a quick access 2 piece mufflers for replacements of burnt out fillers.
https://www.burnsstainless.com/ultra-lightmufflers.aspx
These mufflers are high quality and not crap like the stuff you find on Jegs and other wholesale sites. If you want a custom tubi exhaust, this is the company to go to.
The design has gotten a pretty bad reputation by cheap crappy designs, but major racing teams still use packed mufflers for tracks with sound restrictions.
please note- for a larger
pitch reduction, you need a larger width outer tube.
This is the primary flaw of most of the crap off the shelf designs.
Steel scrubs will give you a more raspier tone over glassmat, but work a lot better with increased heat and last longer. Burns mufflers range from 250-400.