Porex clunk/filters are better than felt type filters, at same price but some advantages.
Many chainsaws shops are replacing felt filters by porex filters, and now it's difficult to find the felt type. ( here in my country).
You can find the best clunk/filter on e-bay ...
http://cgi.ebay.es/ws/eBayISAPI.dll?...m=390287846515
When you try one , you will never want to use a felt type anymore.
Regards