HEPA is widely considered the gold standard when it comes to air filtration, especially for those patients suffering from allergies. What many people may not realize is that there are air filters even better than HEPA called ULPA. HEPA removes 99.97% of particles 0.3 micrometers or more. ULPA removes 99.999% of particles 0.12 micrometers or greater. ULPA is correspondingly much more expensive. Here are some HEPA filters sold on Amazon.com: Here is an ULPA unit sold on Am…