It's not a cloth patch, Wendy. It's a (near) weightless piece of dacron filler from a fabric store.
Many people do this, but I suggest you
not use nearly as much as he did, and instead "stretch out" a much (much) smaller piece until it's nearly vacuous. Then with a pair of tweezers insert the
bottom of the dacron to the powder and then gradually move the tweezers up the filler column to push it into the case uniformly (not 'packing' it as shown). Leave the top of the filler high enough to where the bullet does the final push-down and so have a continuous filler: bullet-base to-powder. NO gap.
I also recommend that you find a
kapok-filled pillow at a used clothing store (or wherever) and use that instead of dacron. It is a natural fiber that is completely consumed instead of being shoved out of the barrel largely intact upon firing.
Last, I recommend you use a standard
roll-crimp die rather than the "factory crimp" Lee as shown in the video. The Lee effectively swage-sizes the case --
and the bullet -- in its operation.
Cast bullets, especially, don't like that at all.