What is Pop Filter?
A pop filter is a screen placed in front of a microphone to disperse the blasts of air from plosive sounds like P and B, which would otherwise register as loud thumps.
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Two designs dominate: a mesh screen stretched over a hoop, and a perforated metal shield. Both break up the air pressure from plosives without greatly affecting the rest of the frequency range. A foam windscreen slipped over the capsule does a weaker version of the same job and also reduces room breeze.
This matters because a plosive is one of the few recording problems that is genuinely hard to repair afterwards. A thump sits on top of the word it damaged, so fixing it usually means a high-pass cut or a volume dip that leaves the word sounding odd. Preventing it at the microphone costs nothing in post.
Mount the filter a few centimetres in front of the capsule and speak at a hand's width from the filter, slightly off the direct axis so the hardest consonants pass to the side of the capsule rather than into it. If thumps persist, check whether the microphone stand is picking up desk knocks, which a pop filter does nothing about.
Where Pop Filter shows up
You will meet Pop Filter most often while comparing podcast recording software - Riverside, Squadcast, Zencastr, and Cleanfeed all deal with it, though not in the same way or at the same price.
Related terms: Double-Ender and Multitrack Recording.