We purchased these bags for the first time in May 2001.  I installed a bag and thought it worked OK.  (I did not throw the former bags, not Hoover bags, out.)  The next time the bag needed changing the lady who cleans the house (unbeknown to us) installed the bag we had been using previously.  My wife who is very sensitive to house dust recognized the difference.  After a very short time my wife said she could smell the dust when the vacuum cleaner was in use.  I changed the bag in our vacuum back to a Hoover bag and the probem was cured.  While not very scientific, it convinced us.  I have thrown the other bags away.