Have to disagree with both simultaneous posters. Pop filters protect the mic from puffs of air generated by aspirated consonants, particularly the letter "P". Just put your hand right in front of your mouth and do the "Peter picked a peck of pickled peppers" thing. This puff of air causes the mic to "pop", and some are more prone to it than others. (Oktava MC012 is a virtual popping machine).
Sibilance is the sound made when air passes between two or more surfaces adjacent to each other or touching, and does not involve the puff of air generated by aspirated consonants, which is also called a "plosive". Sibilance is most often associated with the letter "S", but can also be excessive with consonants such as "F", "TH", or "K". A pop filter won't do diddly about it. Moreover, you *have* to have some sibilance, or there would never be an "S" sound. The key is controlling sibilance, not eliminating it.
There are 2 ways to control sibilance- the right way and the wrong way. The wrong way is called a de-esser, and is a specific form of frequency specific compression that limits the volume of the approximate frequency range of that annoying hiss. Some de-essers use only EQ, and no compression, which is why some people will say it is a form of EQ, and others a form of compression. The better they are, the more they cost, and the better they work. Any de-esser also removes perfectly good sound that you didn't want removed, but sometimes it's better than listening to someone hiss like Sylvester the Cat ("Sssssufferin' Sssssucotash").
The right way is to simply *think* about your damned "S"'s, and soften them, shorten them, and lighten them up. When I say this, I am almost always jumped on by somebody who can't be bothered to modify their bad mic technique and their lousy diction, because they might lose that glorious emotional groove. What this usually means is they are too lazy to develop the discipline to modify their enunciation so the mic won't pick up excessive sibilance. In short, it's cheaper and sounds better to simply stop hissing like a snake when you sing, than it is to use a sophisticated box to try and cover up your bad technique.
I'm sad to say that I had to use a de-esser for quite a while after I was forced to wear dentures. That plastic or metal palate just isn't like the nice soft flesh of the roof of your mouth. Later, I had a set made with a pricey gold palate, which is a fifth of the thickness of the acrylic palates that most dentures have, and I have not needed to turn on the de-esser since I got the new teeth. I did, however, have to change the way I prounounce nearly every word. It took me about 3 months to normalize my speaking and singing voice. Woo Hoo!-Richie