What first struck me about IBM Plex Sans was its form. It’s not the first typeface in which right-angle interiors contrast with smooth exteriors. But it does achieve a remarkable balance of this effect, applying it overtly to some shapes — the tail of the a, the ear of the g — and far more subtly to others, with the straight segments of the bdpq bowls.
It’s the kind of detail you could see getting ironed out in the process of designing a typographic system for one of the world’s largest corporations. But if anything, Plex’s design team (helmed by Mike Abbink) turned up the volume as they moved on to the monospace.
Short horizontal sections from the sans extend to increase the width of the f, j, and t, culminating in severe lines in the lighter weights of Plex Mono. Some of those right angles become acute in the monospace italic, as letters gain spectacularly sharp outstrokes.
As Plex’s impressive specimen site makes clear, these formal decisions are rooted in IBM’s history. The right angles come from the square counters in the IBM logotype’s B, while Abbink and company were inspired by the IBM Selectric Typewriter’s Italic 12 for the Mono Italic. Plex Serif descends from the Bodoni that Paul Rand preferred in his famous collaboration with the technology company.
This is the kind of type design, or design in general, I love the most — discerning visual quotation that simultaneously anchors a design in history and provides solutions to the current use case.
What might be Plex’s most remarkable aspect, though, is that it’s open source; the goal is for it to become a standard operating system typeface. Given IBM’s credo that “good design is good business”, the decision to make Plex open source is yet another appropriate quotation.