Mechanical Keyboards 101, Part Four: Key Caps!

Posted: April 3, 2017 in keyboarding

We’ve talked about quite a few topics thus far in this series. The basics of mechanical keyboards, the switch technology, the shape, size and layout of the various options.

But…yes, you’re right to be afraid…there’s more. Just as important as the shape of the ‘board and the mechanics of the switch, arguably, is the key cap. It is, after all, the point of contact between the organism and the machine. It’s where the feel of the keyboard is determined.

Let’s dig into the topic.

Key Shapes:

Square and Conical: This is the most familiar shape with modern keyboards. There’s some variation among this key shape, which tapers from the completely square base to a somewhat rounded or chamfered top. This variation is how high the key cap sits above the switch, how much space between the key caps there is when they’re in place, and the amount of dishing for your fingers to get a tactile feel of being “home”.

A significant number of newer keyboards tend to be pretty flat on the top of the key caps. This can allow them to be a bit shorter, with a slightly larger area of engagement for the fingertips, but it doesn’t quite give the same level of feeling in terms of being right on the key, rather than off into a corner.

Older keyboards tend to have taller key caps, more dishing, and slightly greater space between the face of the key caps. This gives them the look of having smaller keys, although this is not really the case. In my experience, you can adapt to different key caps, just like any other dynamic of the keyboard, but you’ll probably have your favorite, after some A/B testing. This will probably have a lot to do with what you’re used to, though preferences can change over time. As with any device, it’s usually wise to give a new keyboard some time to grow on you. I’ve had a few that were not to my tasted at first, but ended up being a favorite in the fullness of time.

Most “full stroke” keyboards will have squared conical key caps. These are equally found on membrane and mechanical keyboards, as they have long been the standard. Due to the constraints of mechanical keyboard construction, you can’t get altogether away from a high loft on the key cap. If you see a very low profile key set that differs from what would be “normal”, it is likely a rubber dome model. (Note: this is changing, as a few manufacturers are working on low profile mechanical switches. It has yet to be proven that this technology will provide a good typing experience.)

Sperical: Unlike the square-ish keys we are familiar with, these switches are round or oblong in their shape, tapering to a squared-off lower section, where they interface with the switches. These types of key caps are more frequently seen on older keyboards, but there are a few models that use them to this day. A fairly small group of keyboards will feature this key shape, however.

This type of key cap is often deeply dished, so that your fingertips almost nestle down into them if they are at rest on the home row. I haven’t typed on this type of key type that often, but the typewriters I learned on back in the day had this type of key cap.

Spherical keys are often fairly tall above the switch, and the nature of the shape will often cause them to have more mass than their square counterparts. Because a more rounded shape can often have a slightly higher torsional strength than a squared shape of the same mass. Rounded shapes tend to have less vibrational resonance modes, such that they won’t be as likely to add an odd overtone or unpleasant noise to the typing experience.

Something you’ll often see on a sperical key cap is that they have fairly large legends on them. These are typically centered. I think that this is primarily due to the simple fact that, in a round shape, having something off to one side tends to look poorly done to the eye.

Here and there, you’ll see keyboards with altogether circular keys, but they are not common. I have a small bluetooth keyboard with this sort of keys, and though I was initially concerned with this being a major technical hurdle, it turned out to feel just fine. They keys were, strangely, just where they were supposed to be. Once again, I was proven to be a poor oracle. Perfectly round keys are rarely seen on normal keyboards, however, because trying to institute them to good effect with the height and spacing of said designs can encounter some technical hurdles, both from the design and utilization perspective. They do exist, however.

Flat Top: In this day and age, it’s not at all uncommon to see desktop keyboards with fully flat keys. Some of them are traditional, low profile key caps, while others are essentially disembodied laptop keyboards, with a scissor mechanism over the top of a membrane matrix. If you are adroit with a laptop keyboard, these may be fine. Their quality is greatly variable. Some are absolute trash, some are usable. They are not, however, mechanicals, and so they lack the wonderful magic that we’re looking for.

There are also faux-vintage keyboards that use key caps that mimic ancient manual typewriters. I have not had a chance to try one of these, as they are typically somewhat expensive. I wonder if, in order to cleave to a stylistic choice, they give up a little in terms of utility. I’m sure, however, that you can get used to the feeling. Let us be honest. More than a little of this is in the heart and in the spirit. Feels may be somewhat more important than reals, when it really comes down to it. I should also mention that these faux-vintage keyboards are often created with rounded or oblong keys, the better to appear old-timey.

Key Cap Material:

The material that key caps are made from will have some impact upon how they sound in use. The material will also dictate how the keys behave under stress. The thickness and accuracy of manufacture is a large consideration, as well. Thus, there is disparity between keys made with the same material. In almost all cases, more material tends to yield a better product, with higher durability and a more pleasing sound in use.

ABS: This is the most familiar type of plastic used in key caps. Acrylonitrile butadiene styrene is a flexible, easy to manipulate thermoplastic that is very sturdy. The vast number of full-stroke keyboards use this material. It is inexpensive, and has as much durability as most keyboards of today require.

Most keyboards, even expensive mechanicals, use ABS in the modern era. It can be imprinted with most of the methods I’ll discuss below, and is able to, with the correct methodology, keep its key legend through a vast amount of use.

ABS does have a few disadvantages, however. The first of these is that the material tends to create a fairly slick surface. It does not typically feature a tactile surface texture that some other key materials do. Thus, if you tend to feel like you’re sliding around and don’t have as much surety in engagement as you’d like, ABS can be less favorable for you.

The second issue with ABS is that it tends to “shine up”. It is likely that you’ve seen an old keyboard around an office that has keys that give a high shine, especially where someone’s thumb acted upon the space bar. This is a hallmark of ABS key caps. The material, though tough under impact stress, is not very hard at its surface. That means that, as it abrades, your fingers will almost have the effect of waxing down below the normal surface, creating the shallowest of swales in the plasic. This becomes embedded with skin oil, and you’ve got a shiny spot. It can be slightly improved with a wash and a scrub, but the shine will come right back. Once the plastic is shiny, it has a bit of wear. Because of that ablation of the surface, some types of printing will wear away faster on ABS. Unless your keyboard is used with a great vigor, however, the material will likely last you for many years before siginficant degradation will take place.

Finally, ABS is not natively very UV resistant. It will discolor in the sun. If you’ve seen an old piece of computer equipment, nominally having once all been one color, but now sporting multiple different shades of dirty beige, that means that there are plasics of different compositions being used for the different pieces. The ones that are seriously yellowed are probably ABS. The better grade of ABS will be treated with some manner of UV resistant coating.

PBT: Often considered the best material for key caps, Polybutylene terephthalate is a harder but more brittle material, when compared to ABS. Most of the storied keyboards from the old days used this material. Today, the swankiest of the mechanical keyboards you’ll find still use PBT. In addition, key cap sets of this material can be purchased for the dominant key switches of today.

What is it that makes PBT favorable over ABS?

First, PBT key caps will often be manufactured with a nice tactile texture on the key tops. It gives the keyboard a feel and confidence that a slippery key cap just doesn’t provide. Because it is a much harder material, the texture that is typically present (they can be smooth, if the manufacturer wishes) will typically survive a vast amount of use without wearing down.

PBT is also highly resistant to getting shiny in use, so that an old, well-used ‘board can look almost new after being cleaned up.

PBT is not photosensitive, so there is no concern about the key caps yellowing with age. I should mention that black or very dark-tinted plastic of any formulation tends to be pretty color-fast. This is very possibly the reason that black plastic became the norm in the industry as the 90’s wore on.

Finally, it should be mentioned that PBT is much more thermally stable than ABS. If one puts ABS into boiling water, the keys will partially melt and no longer fit properly afterward. PBT does not have this issue.

Because PBT is more brittle, many makers tend to engineer a slightly thicker key cap. This will often result in a more substantial feel, and a different sound when typing. A significant amount of the noise in a keyboard is that of the key hitting the base plate and then returning to the top of its travel. A very thin material can result in a “cheap” or unsatisfactory sound at times. There are a number of thick-molded ABS keys, so PBT does not hold a lock upon this market.

POM: Polyoxymethylene plastic can be used in key caps, but is quite uncommon. I don’t know of any keyboard manufacturers producing a key cap of this material at this time. There may be a few out there, but they are not well-known.

You’re more likely to see POM in things like guitar picks, electronics and various other machine parts. I gather it’s an exceedingly tough plastic, but it may not be the best for keyboards. The usage cycle of a key cap man not benefit from some of the things that POM does well.


It is likely that you’ve owned or worked with keyboards that have had an issue with the print fading, darkening, or completely coming off of some of the keys. That, without being too facile, is not the outcome we’re hoping for.

There are a number of ways to create the legends on the keys. They all have their place, and their set of assests and liabilities.

Pad Printing: This is what it sounds like. The legends are printed on the keys with a flexible printing head. It’s sort of like printing something on a T-shirt. This type of printing, because it’s simply a deposit on top of the key, can wear off, either with chemical etching (because of that hand cream you like so much), or because of mechanical wear. Although we don’t think about them in this way, our fingertips can serve to put a significant amount of abrating force on a tool, when we have our hands upon said tool for hundreds of hours. Pad printing can be the victim of such a grinding force.

The upside, though, is that it’s cheap, easy, and can be done in any color you like, with any legend you can imagine.

Amost every keyboard you look at, if it is less than fifty bucks or so, will have pad printed keys. They’re okay, but you know that you’ll have the chance of the key legends fading or otherwise having an issue.

Laser Etching: Here, we step up to a whole different level of durability. The legend, in this case, is actually burned into the key cap. This can take one of two forms. The first variant is a thermal process, where the shape of the legend conforms to the “burn” of the laser, and the color portrayed by the legend is created by the natural discoloration process of the plastic format (darkening or lightening). The second methology possible is to actually create a small trough in the shape of the legend on the key, then “in-fill” a contrasting material into that space. I assume that the in-fill material is some kind of plastic or plastisol material, though that isn’t clear to me.

Laser Etching can, under extreme circumstances, become little bit indistinct around the edges, but it won’t wear off altogether.

Dye Sublimation: Rather than burning into the key cap, this method utilizes an energetic process that allows a dye to be infused directly into the key cap’s molecular structure. This is done in such a way and to a depth that assures that there is no way to have the key legend wear away. I mean, provided you’re not using your keyboard with a bench grinder, anyway. Dye Sub printing is considered to be right up there with the best you can get. The vast majority of PBT keycaps are printed in this way.

Double-Shot: This is the absolute most rugged of all methods for showing a legend on a key cap. Why? Because it’s not actually a printing method at all. Two seperate pieces of plastic are actually fused to portray this legend, then the finish work is done to make sure the cap is the right size and shape. Basically, you have one color of plastic as the “underside” part. This is the color that the legend is going to be. The key top plastic is a contrasting color to this. The two parts are mated together, such that the legend is actually the material of the underside material being shown through the key top.

Most of the time, double-shot methodology is only employed with ABS, as it is easy to work with, and this is by far the most reliable way to make a durable legend, given ABS’s qualities. A company called Tai Hao is currently making double-shot PBT caps, however, so it is technically feasible. A few other brands are doing this, as well. They vary greatly in price, and I haven’t seen any but the Tai Hao brand, so I can’t comment upon the relative qualities of these offerings.


While having an LED backlight beneath a key is not specifically something that will have any impact on the performance of the ‘board, a significant number of mechanicals do feature this technology.

Traditionally the province of gaming keyboards, backlighting can help to find your way to the correct key when the ambient lighting of your room is low. While touch typists endeavor to keep from looking at their keyboards any more than necessary during the typing action, locating the home row can still be made easier if the legends of the key caps are brightly illuminated.

As I alluded to, the backlighting on keyboards is provided by LEDs, which is to say, light emitting diodes. Some of these are capable of only one color, while the RGB style backlights are able to produce millions of colors. Some are on/off, others can light specific keys, as you see fit, and the most complex of them have a small processor inside the keyboard that can give you any number of patterned or reactive lighting schemes.

I have, thus far, not had any real interest in a backlit keyboard, but I may procure one at some point, if only to see what it’s all about, as it were.

As you might imagine, the key legends have to be transluscent in order to the light to shine through. This means that the key caps have to be made with a more complex process. My impression is that the most common method to create the translucent key legends is to use the double-shot technique, with the underside plastic being the bit that lets the light through. It is possible to mold the whole cap from a translucent material, then paint it, but that’s really cheaping out, and asking for a bad result.

On older backlit ‘boards, you’ll sometimes see models that have a backlight, but it will shine around the outside of the key caps, rather than through them. This is probably less expensive, as it can be used with any key cap style.

It should be noted that LED backlighting is not a new thing. Older keyboard generations ofen had an LED that shined through a cutaway on a keys such as the num lock and the caps lock keys.

Summing Up:

In the current age of throw-away keyboards, most examples will be designed to simply be good enough. They will last a year or two, and then go away, to be replaced with the new thing, which will also be thrown away soon enough. If you like to have your keyboard be your stalwart friend, with you through the lean times and the flush, outliving computer after computer, the differences in keycap technology will begin to become important.

I recently replaced the key caps on all of my older mechanical keyboards. Being Cherry MX equipped devices, it was easy for me to find replacement sets. For one set, I ordered the whole set directly off of Amazon. For the other two, I designed custom color schemes and legends at a site called WASD keyboards. After pulling all the key caps off of my old ‘boards, cleaning them thoroughly, and installing the new caps, they are almost new. In some ways, better than new, because they have more “personality” than they had leaving the factory. This customizability, this ability to disassemble, service, and repair your fondly-held devices, is another great advantage of the mechanical switch keyboard. It doesn’t have to be throw-away. It can be a keeper, and you can hot rod it as you see fit.

Well, that wraps up my series of articles on mechanical keyboards in general. From here on, I’ll be posting some reviews, thoughts, and updates as I learn more and find elements of this hobby that I think you’ll enjoy knowing about.

Cheers, and happy typing.

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