The character's mouth is visibly packed or being packed with socks, underwear, handkerchiefs, or some other form of cloth or solid material. A thoroughly-packed mouth can result in cheek bulge.

It should be noted that cleave gags, OTM gags, and OTN gags are not very effective on their own as the gagged person can freely move their lips, tongue, or jaws. Cleave gags and OTM gags in addition do not cover the nose and thus do not muffle the noise coming through the nose. Mouth packing can restrict movement and muffle sound, but can easily be spat out or pushed out by the tongue if not secured. Combining mouth packing with the aforementioned gags is far more effective by restricting lip, tongue, and jaw movement, and by muffling sound coming through the mouth. OTN gags, especially multiple and/or thick layers, also muffle noise from the nose, reducing sound much more effectively.

Tape gags are also frequently combined with mouth packing, and are especially effective when the tape is wrapped completely around the head as opposed to simply placed across the lips. Characters with elongated jaws can also be muzzled to force the jaws closed.

In many instances of the aforementioned gags, it might be assumed that the character's mouth is packed, but a picture should only be tagged packed mouth if the packing is actually visible, shown as part of a gagging sequence, or strongly implied through a bulge in the gag.