True HEPA vs HEPA-Type

This page is short because the point is small and specific — and because once you know it, a lot of packaging reads differently.

HEPA originated as a specification for filter media, with defined efficiency at a defined particle size. In industrial and medical contexts it is tested and certified per filter unit. In the consumer air purifier market there is no equivalent enforcement, and “True HEPA” emerged as a way to signal “this is the real thing, not the cheap imitation”.

The difficulty is that nobody adjudicates it. There is no body a manufacturer applies to for permission to write “True HEPA” on a box, and no test the phrase commits them to.

Both certification registers record a filter classification per model, and it distinguishes HEPA from HEPA-Type. That is a real, published, checkable field — and it does not always agree with the packaging.

Do not use it as a primary filter. CADR already contains filtration efficiency, because it is a combined measure of efficiency and airflow — so a HEPA-Type machine with 435 certified CADR is delivering more clean air than a HEPA machine with 109. The outcome measure beats the input measure.

Use it as a tiebreak. Between two machines with similar certified CADR, a similar certified room size and similar running cost, the HEPA classification is a reason to prefer one.

And use it as a check on the marketing. A box saying “True HEPA” over a register entry saying HEPA-Type does not mean the machine is bad. It means the phrase on the box was not making a promise anyone is holding the manufacturer to, which is worth knowing generally.

Claims about capturing ever-smaller particles — 0.1 microns, 0.003 microns — are describing a regime where filtration gets easier, not harder. Efficiency has a minimum around 0.3 microns because that size is too large for efficient diffusion and too small for efficient interception; both larger and smaller particles are caught more readily. The physics, laid out.

So a manufacturer boasting about 0.003 microns is boasting about the easy part while implying it is the hard part. That is the pattern this page is really about, and the filter classification is just one visible instance of it.