You might be wondering how keycaps are made. The crisp, durable legends, two layers of plastic, and vibrant colors seem extremely exotic for these small pieces of plastic - that's part of why they're so expensive! In this article we will take you through the process of creating keycaps.
A common method of keycap legending is called dye-sublimation. During the printing of legends on the keycap, ink in the shape of the legend is pressed into the keycap, and then subjected to very high temperatures. When the process is over, the ink has fused thoroughly with the keycap. This is a relatively cheap method of keycap legending that allows for different shapes/pictures on keycaps without having to create completely new molds. Additionally, the colors of the legends have the potential to be quite crisp, depending on the manufacturer. The downfall of this legending method is that it is impossible to sublimate light text onto dark plastic. For example, you can have a set of black text on white keycaps, but not white text on black keycaps. This is where reverse dye-sub comes in.
Reverse dye-sub is the same as dye-sub, but the colors around the legend are colored instead. This allows us to bypass the light-legend problem while maintaining the wide variety of colors available with dye-sub. However, with reverse dye-sub, you have to cover a lot more surface area as well as the sides of the keycap. This makes it noticeably more expensive than dye-sub. Reverse dye-sub is mostly used when there are either many novelties, uncommon colors (for example bright orange), or different fonts than normal.
Widely considered the highest quality method of legending keycaps, double-shot keycaps consist of an outer layer of plastic that provides the general color of the keycap, while the inner layer is the color of the legend and peeks through the upper layer to form the legend. The fact that the legend is a different piece of plastic makes it extremely durable, even more so than dye-sub. All of the highest quality keycap offerings, such as ePBT and GMK keycaps, are double shot.
Commonly combined with the dye-sub process, PBT (polybutylene terephthalate) is a rigid, tough plastic. It provides a strong and full sound signature (although this depends more on the profile of the keycap), and lasts for years without even shining. The downside of PBT is that it does not show colors as vibrantly as ABS, and is prone to warping, making it difficult to produce thick double-shot PBT keycaps. This is why GMK and ePBT use ABS, as well as the fact that more crisp, vivid legends can be produced with ABS. However, the toughness of PBT can be utilized beautifully with dye-sublimation, as dye-sub can bring color to PBT without having to have double-shot keycaps.
ABS (acrylonitrile butadiene styrene) is a plastic that is easy to mold and produces rich, beautiful colors. This is why many high end keycaps use it for brilliantly-colored keycaps. It combines especially well with double-shot technology and thick walls, since it rarely warps. Its downside is that it is not as UV resistant as PBT (it will yellow over the years), and also begins shining after a year or so of heavy use on often-used keys such as the spacebar.
So What Should I Use?
Honestly, it's up to you. The day-to-day use is not affected much by which of these processes/materials you pick. Knowing the different materials and processes is useful for comparisons, but at the end of the day, I would pick what is in your price range and has an appealing profile and look to you. For some that may be a high-end, bright GMK set, and for some that may be a set of reliable PBT dye-sub keycaps. That's the beauty of the keyboard hobby - it's all up to you!