* Non-existent performance at filtering 0.3-1µm particles, which are more likely to lead to chronic lung-related conditions.

* Extremely poor performance at filtering 1-3µm particles, which are more likely to cause various respiratory problems and other health and productivity issues.

* Terrible air permeability. The lower the permeability score, the more strain the filter would put on your equipment which can dramatically increase the cost of operating your furnace, air conditioner, and heat pump.

* High maintenance. Requires frequent replacements.