A typical mechanical keyboard is comprised of seven major components: PCB, case, plate, switches, cable, and keycaps. Of all these components, keycaps dominate the visual aspect of keyboard design while also accounting for most of the cost in high-end custom mechanical keyboards. However, their impact isn’t restricted just to the aesthetics or cost – they also dictate the all-important touchstones of ergonomics, typing feel, and sound for mechanical keyboards.
You can’t truly customize your mechanical keyboard until you familiarize yourself with the finer nuances of the expensive and confusing world of high-end keycaps. This guide will not only give you a lowdown on keycaps but will also explain the science behind why certain types are inherently better than the others.
Note: now would be a good time to read our primer on custom mechanical keyboards to familiarize yourself with the fundamentals required to make sense of the rest of this guide.
Form Factors and Layouts Shape Keysets
In the custom mechanical keyboard space, keycaps are sold in the form of sets. These keycap sets feature individual keycaps sharing common color and design themes. Choosing custom keycaps is fairly complicated owing to the sheer number of variations in keyboard form factors and layouts therein. That also makes it important to understand these concepts.
The traditional full-size keyboard is comprised of various clusters of keys, namely alphanumerics (alphas for short), function row, navigation (nav) cluster, and numpad. It forms the foundation upon which all custom mechanical form factors are derived. Expressed in percentages, these form factors range from 40 through 100 percent, with each one named relative to the percentage of the full-size keyboard.
Remove the numpad off a full-sized keyboard, and you get the tenkeyless (TKL) or 80 percent form factor. The 60 percent keyboards further drop the nav cluster and function row, with 40 percent variants doing away with the number row as well. If that wasn’t confusing enough, there are multiple layouts within the same form factors.
In simple terms, if form factors roughly correspond to the physical size of keyboards, the layout affects the position of the keys within the same form factor. A 60 percent keyboard can come with or without arrow keys, radically changing the key layout and causing compatibility issues. Then there are winkeyless (WKL) layouts and ones with stepped Caps Lock and split Space Bars.
Dividing Keycap Sets into Kits
All that is just the tip of the iceberg. The sheer number of variations between layouts and form factors make it a nightmare for any single keycap set to cover even the most popular custom keyboard varieties. Thankfully, keycap sets have a clever means to covering a surprisingly large array of keyboard layouts and form factors.
The solution involves dividing each keycap set into a collection of individual kits that build upon the base kit. Most base kits support common keyboard form factors, such as the 60 percent and TKL in the standard ANSI (American) layout. Modern base kits increasingly include support for the increasingly popular 65 percent keyboards as well.
Additional kits add coverage for full-size keyboards by including a separate numpad kit. Live across the pond? You may want to purchase the ISO kit. This concept of offering an additional bunch of keycaps in the form of extension kits allows everyone – from those who seek arrow keys on their 60 percent keyboards to Dvorak afficionados and 40 percenters – to use the same keycap set on all keyboard variants.
Keycap Sizing and Its Impact on Layouts
Keycaps are measured in a relative scale where the alphanumeric keys form the basic unit of measurement. These are the smallest keys on the keyboard, such as the numbers, letters, and arrow keys, and are considered 1u keys representing one unit of keycap measurement. Every other keycap size is represented in terms of how many 1u keys can fit into their footprint.
The Backspace, for example, measures exactly as much as two 1u keycaps combined. That makes it a 2u keycap. The Tab key is one and a half times as wide as 1u keycaps, thereby making it a 1.5u key. The Enter keycap is 2.25u and the Space Bar is usually 6.25u. The key word being “usually,” because different keyboard form factors and layouts can have the same keys, such as the Space Bar in sizes ranging from 2.25u to 7u.
Some keycaps come in different sizes across varied layouts for reasons ranging from ergonomics to optimization of key density. Comparing three different layouts of the same 60 percent keyboard is the best way to understand this concept. The first three rows of all three layouts pictured here are identical, but the bottom two rows are vastly different.
On one hand, you have the standard 60 percent ANSI layout sans the arrow keys, whereas the other two layouts feature dedicated arrow keys. The layouts with arrow keys achieve that feat by significantly reducing the size of the left and right Shift keys in the fourth row while also shrinking and outright eliminating modifiers in the fifth/bottom row.
How Math Dictates Layout Choices
It’s all down to simple mathematics. Each row of keys on a 60 percent keyboard is 15 units across. The 60 percent ANSI layout (below image) has seven 1.25u modifiers and a 6.25u Space Bar on the bottom row. That’s a total of eight keys. The other two layouts with dedicated arrow keys have a total of nine instead. They achieve this by borrowing a quarter of a unit from the four 1.25u modifiers on the right side of the Space Bar to make space for an additional key.
The third row of the two layouts with dedicated arrows is where things get complicated. The bottom-most layout has the [?] key missing while sporting a larger left (2.25u) and right (1.75u) Shift keys. The layout in the below image (Split Shift), on the other hand, retains the [?] key while reducing the left and right Shift sizes to 2u and 1u, respectively.
Some choose the Split Shift layout because they prefer direct access to the ? key. Others still insist on the Regular Shift layout because the standard 2.25u left Shift has better compatibility across keycap sets compared to the non-standard 2u Shift found on layout A.
This is an important consideration, as most base kits lack 2u Shift keycaps, which usually requires spending another $30 to $50 on a compatibility kit containing that particular keycap.
Understanding Keycap Profiles
When viewed from the top, keycaps appear to have the same shape across different sets. This is because they share the same dimensions (length and breadth) across all sets. The main dimensional diversity between keycap sets is only ever evident when viewed along the sides. That’s why the term keycap profile is used to denote the shape of the keycaps.
The concept of keycap profile basically refers to the outline as it appears in the profile view – that is, when the keyboard is observed sideways along the rows. Look at different keycap sets from this angle, and it is apparent that some are tall and concave, whereas others are short and flat. Some keycap sets share the same shape across all rows, whereas others exhibit a distinct shape for each row.
Keycap sets are classified into profiles that determine these parameters, which include height, sculpt, and surface geometry. Keycap profiles such as DSA and Cherry are short, whereas SA and MT3 profiles are significantly taller. This is an important consideration for smaller form factors such as 40 percent keyboards, where portability is paramount. Otherwise, taller keys generally tend to be more pleasant and ergonomic to type on.
Surface Geometry and Typing Accuracy
The surface geometry of individual keycaps also varies between different profiles. Laptop keyboards are equipped with keycaps exhibiting perfectly flat surfaces to reduce overall thickness. However, this has a negative impact on typing speed as well as accuracy. This is evident as soon as you move to Cherry profile keycaps which sport a cylindrical depression along the top surface.
The human fingers have an incredible capability to relay accurate positional information back to the brain. The sides of these keycaps with cylindrical tops are higher compared to the center, which is at the lowest point. Your fingers subconsciously relay this depth information to the brain. This, in turn, allows it to determine the exact point at which the finger hits the keycap and make corrections on th fly, just by the virtue of touch.
That also makes the MT3 and SA profiles inherently superior, because their spherical/concave tops enable the fingers to relay spatial feedback along both X and Y axes. Combine this with a larger gap between adjacent keys, and you get keycap shapes that enhance typing accuracy. That’s also why most touch typists are significantly slower on laptop keyboards compared to their mechanical counterparts equipped with nicer keycap profiles.
Uniform vs. Sculpted Profiles
Keycap sets with uniform profiles exhibit the same shape and height across all rows. Those with sculpted profiles have different shapes and heights for each row. Keycap sets with uniform profiles have two primary advantages. Their height uniformity allows them to be uniformly short, which is great for compactness and portability.
The lack of variation between rows also means that modifier keys can be moved around across different rows, thereby making layout compatibility easier. You can also rearrange keycap sets with uniform profiles to achieve esoteric layouts, such as Colemak and Dvorak.
Keycap sets with sculpted profiles aren’t as flexible with layout compatibility. Because each row has its own shape and height, it is impossible to move around modifiers and rearrange the alphas to achieve different layouts. This makes it mandatory to buy additional compatibility kits in order to use diverse layouts.
Sculpted profiles, however, make a significant impact on typing accuracy as well as ergonomics. Since our fingers rest on the home row in the middle of the keyboard, accessing the top and bottom rows is difficult, as they are located much further away. Sculpted profiles minimize the distance between these rows by modifying the angle and height of the keycaps along rows.
Just like surface geometry helps with typing accuracy, sculpted rows enable touch typists to easily tell which row they are on without looking at the keyboard.
PBT vs. ABS Keycaps
Barring exotic and uncommon materials such as POM (polyoxymethylene), PLA (polylactic acid), rubber, and aluminium, keycaps are primarily fashioned out of ABS (Acrylonitrile Butadiene Styrene) or PBT (polybutylene terephthalate). ABS is common because it is cheaper to manufacture compared to PBT. This is primarily because, compared to ABS, PBT melts at higher temperature and shrinks to a greater degree when cooled.
While that makes PBT keycaps harder to manufacture, that also means it’s a denser material that’s significantly more durable than ABS. This is rather important because human fingers are capable of applying a significant amount of abrasion to keycaps owing to the sheer number of keystrokes hammered over the course of time.
ABS Shines Faster: This gradual abrasion tends to polish the softer ABS plastic on the keycaps to the point that the surface attains an unsightly shine. Because PBT is denser and harder than ABS, the former takes a significantly larger amount of time to develop the shiny surface associated with worn keycaps. Having said that, manufacturers tend to work around this problem by texturing the keycap surface to delay the eventual shine.
PBT Keycaps Tend to Exhibit Bowing: On the downside, the higher melting point and rapid shrinkage of PBT not only makes it expensive to produce, but the longer keys such as Space Bar, Enter, and Shift aren’t somewhat difficult to manufacture straight and true. That’s why PBT keycaps tend to have higher alignment issues with stabilisers compared to their ABS counterparts.
ABS Usually Has Better Colors and Crisper Legends: The ease of injection moulding ABS plastic allows manufacturers to try complex fabrication techniques, such as doubleshot legends, which involves forming legends using contrastingly colored plastic instead of dyes. Some keycap manufacturers also achieve this feat with PBT, but that’s quite rare and expensive.
PBT keycaps instead commonly use dye sublimated legends that are almost as durable as doubleshot ones but not nearly as sharp or colorful. There are other legending techniques, such as pad/UV printing and laser etching, but these are too low quality to be used in any decent custom keycap sets.
Keycaps also greatly affect the overall keyboard sound signature. However, that’s too complicated a subject to cover in this guide.
Try to avoid getting caught up on PBT vs. ABS arguments because actual keycap quality depends on parameters such as color accuracy, keycap thickness, legend quality, and manufacturing tolerances. Great manufacturers such as GMK make terrific ABS keycap sets that can put most PBT counterparts to shame.
The real charm of this hobby lies in spending an obscene amount of money trying out different types of keycap sets to figure out what you like. Everything else is a matter of opinion and personal taste.
For more on this topic, check out how to replace a mechanical keyboard switch on your own,