I am currently working with a company to develop improved exhaust packing for the latest 450 quads which are notorious at destroying typical exhaust packing.
I've been testing various components from this company over extended 150 to 200 mile a day rides.
The first products tested lasted about 600 miles or 25 to 30 hours of use. I am currenly on the second round of testing with a slightly different make-up.
here are some photos of the first components (multiple layers of different materials) tested.
If you run a spark arrestor your packing will usually expire at a quicker rate.
Be aware that with exhaust packing blown out you risk damaging the exhaust can and/or mounting brackets due to overheating.
The company I am working with expects to have a new product out on the market early next year.