Editing Keycap material (section)

==ABS==
Most keyboards in the world have keycaps made of [[Wikipedia:Acrylonitrile butadiene styrene|ABS]]. ABS is short for "Acrylonitrile Butadiene Styrene", being a copolymer of these three monomers. ABS exists in many different formulations for different applications. (Poly)styrene is the main ingredient. Butadiene makes it more flexible and less brittle. Acrylonitrile makes it harder. ABS, and other blends with Polystyrene (PS) are some of the most commonly used plastics for computer equipment, including keyboard cases. 

ABS keys is the preferred plastic for [[Double-shot molding|double-shot molding]]. That is because most other plastics shrink too much in the moulding process. Legends on ABS keys can also be [[Keycap printing#Pad Printing|pad-printed]], laser-etched (burned) or laser-engraved (with or without infill).
Because of the low shrinkage, some keyboards have [[space bar]]s made of ABS even if other keys are made of PBT or POM.

===Yellowing===
[[File:AT102W faded keycaps.jpg|thumb|right|250|[[Dell AT101]] keyboards with a mixture of yellowed keycaps.]]
[[File:IBM 23F3216 front.JPG|thumb|right|250|[[IBM P70/P75 keyboard]] with a slightly yellowed space bar.]]
ABS (and other polystyrene blends) will gradually turn yellow over time when subjected to ultraviolet light, a component of sunlight.

Yellowing occurs faster if the plastic contains flame-retardant chemicals, but it is more often used in the plastic of keyboard cases than in keys. The [[IBM Enhanced Keyboard]] typically used a space bar made of ABS, but sometimes you can find vintage keyboards with a mixture of very yellowed keycaps, and others less yellowed or not yellowed at all. A plausible explanation has been suggested<ref name=yellowing/> and it goes like thus.

Back in the day, components used in the injection machine were hand-mixed and tossed in the injector's funnel. As some of the pellets in the mix were heavier than others, they would go to the bottom of the funnel due to machine vibration, leaving the lighter ones on top. Also, in order to ensure that the final product had the minimal characteristics expected, the operator would put some "surplus"  of flame-retardant in the mix, and since this component was lighter than the pellets, it would tend to stay on top of the funnel, the ending result being pieces where some had more flame-retardant than others, and some might even have none at all.

The main agents triggering the yellowing process are ozone, UV radiation (either by direct sunlight or some lamps), humidity exposure and heat sources. Bad mixed polymers with stabilizing compounds will yellow earlier than others.

Another explanation for specific keycaps being more or less yellowed than others is that they come from a separate batch. A typical example of this are the "F" and "J" keycaps due to the notch or "nub" they have.

Yellowing can be temporarily reversed with the [[Retr0bright]] process.