Average beta rating based on ISO 4548-12 multi-pass test methods:
B100 = 25 (at 25 or greater micron, media is 99% efficient.)
B75 = 20 (at 20 or greater micron, media is 98.7% efficient. Also considered absolute rating.)
B5 = 10 (at 10 micron or greater, media is 80% efficient.)