I always called it a crutch. I just use 3.5x5 in index cards and fold it over once. Cut it to fit the end perfectly around the walls of the joint and have it end (the lenght) right when the joint ends. Really you can use whatever you have around you, improvise. Basically, if I don't have an index card around, I'll look around me for whatever is the closest to what I want. If it's too thin or weak I just fold it over like I do the index card.

I like it because when you get down to the end of the joint, its harder to get a good hit off when its burning your fingers and shit and you're trying to keep a hold of it and at the same time not pinch it too tight so it doesn't close the end of the joint. This way, it keeps then end open so you can get fat hits off while your fingers are somewhat safe(r).

Weed in my mouth isn't really too much of a problem as I usually pack it in well and it's usually sticky enough to say in the joint, besides I really don't mind too much. But for those that do, instead of having the crutch tailor made to the joint, you can just break off more than you need and spiral it around or make an S (less blockage but still ok) and that should keep the weed in pretty well.