Typekit:

Just minutes ago, at the ATypI conference in Warsaw, the world was introduced to a new kind of font: a variable font. Jointly developed by Apple, Google, Microsoft, and Adobe, a variable font is, as John Hudson put it, “a single font file that behaves like multiple fonts”. Imagine a single font file gaining an infinite flexibility of weight, width, and other attributes without also gaining file size — and imagine what this means for design.

A List Apart:

Type is tied to its medium. Both movable type and phototypesetting methods influenced the way that type was designed and set in their time. Today, the inherent responsiveness of the web necessitates flexible elements and relative units—both of which are used when setting type. Media queries are used to make more significant adjustments at different breakpoints.

However, fonts are treated as another resource that needs to be loaded, instead of a living, integral part of a responsive design. Changing font styles and swapping out font weights with media queries represent the same design compromises inherent in breakpoints.

Robin Rendle:

Why would we want this sort of flexibility on the web? Because loading multiple weights and widths is impractical in some cases and outright foolish in most. Yet the ability to stretch and expand a single responsive font file would supply improved performance23, as only one font would need to be requested, and typographic subtlety, since we could adjust the text as we see fit.

Grazie a una collaborazione fra Apple, Adobe, Microsoft e Google, il formato OpenType include ore una specifica per dei font variabili: font che invece di avere un peso predefinito (grassetto, normale o leggero; per esempio) possono calcolarlo e adattarlo partendo da una font family di base, a seconda del contesto.