I use a strip of felt. I run it from top to bottom quite a bit offcenter. It seems to do the trick.

Medium weight felt is (and always has been) the best and most commonly used fabric for dampening for lots of reasons (very porous so it acts kind of "dead" rather than vibrates, compresses well so the bearing edges aren't negatively affected, etc . . )

I just want to ad my $0.02 worth about the positioning.

The "slightly off center" thing is important because it kills harmonic vibrations that are both circumferential and symetrical with respect to the diameter of the drum. If your ran the felt right down the middle, the head could still have resonance (albeit low frequency resonance) from these "side to side" waves.

I think there is a good video out on You Tube that shows the various nodes of vibration of a circular drum head that explains this better than I can. I'll post a link if I can find it.

I went quite a bit further and stuffed my bass drum with a pillow to get a much deader sound - but that's just what I prefer.

I used to use felt strips but now I prefer a pillow in the bottom of the kick drum (I duct tape it to the inside of the batter) that only goes up the head a few inches. And I use one of those large hoop mount external bass drum mufflers on the batter too.

I found that felt strips limited the fundamental, and I can never get enough of that.

With calf heads I don't muffle any of the other heads because the nasty harmonics of plastic don't exist.