Brake Pads, Performance Rings and Turbo Disks are all attempts by manufacturers to defeat the low friction involved in todays modern long spinning ball bearing yo-yos. These yo-yos sleep prodigously, but often are unresponsive. Starbursts (raised bits of material in the gap of the yo-yo) can be used to create friction and increase response, as can introducing lubricant into the bearing, thus slowing the rotational speed of the balls. The adhesive pads mentioned above are another technique used to this end.
Custom Yo-Yo Performance Rings (top right) are a ring of material like rubbermaid tub treads. Due to litigation with Proyo this style of Performacne Ring has been discontinued and replaced with a smooth (non-bumpy) rubber. Proyo Brake pads (bottom left) have a cork appearance but are actually a recycled ruber material (think gaskets). Tom Kuhn Turbo Disks (top leftt) are a thin cloth-like (linen) pad. The Duncan Freehand and SPintastics Great White uses Friction Disks (bottom right) that are thicker than the other systems, and consists of a rubbery surface over a fibrous (furry?) layer.
In addition to these, the SuperYo Samurai uses a ring of rubber like material called lamina for response. Plays well but is short lasting and very expensive.