In September of 2016 a new font format was announced. This format allows multiple styles of a typeface to be contained withing a single font file, which can make for a significantly faster load time on the web and allows for intermediate instances in between the pre-defined styles. The support for this new format is still limited, but it can currently be used in the nightly builds of webkit as well as a free app called Font View.
For my new typeface Dunbar, I created variable fonts with both weight and x-height axes. If you license the Dunbar Tall family or Dunbar Low family bundles, you will also receive the related variable fonts which contain the full range of weights as a single file. And if you license the complete Dunbar series you will also receive a single variable font with the full range of weights and a range of x-heights between Tall and Low, all as a single file.
Because the format is new, it's very likely things will change. I plan to make updates as needed, but for the time being, these fonts are provided “as is” since the format is still awaiting application support. I hope that by providing Dunbar in this new format, it will enrich the typographic pallette of the web and be used in unexpected and unique ways.
As I previously posted (when I made a single glyph variable font): the announcement of this new font format was made by representatives of Apple, Google, Microsoft, and Adobe at the ATypI conference in Warsaw. The new format allows for a single file to contain an entire family, or multiple related families, of font instances. Previously if you wanted to license an entire font family with a range of weights for your website (like Light, Regular, Medium, Bold, Extra Bold, and Ultra) the type foundry would generate a separate font file for each style. But now it's possible for type foundries to put all of these styles into a single file, so the file will be smaller and you'll only have to make a single http request. This file format can also allow for subtle variations beyond the specified instances, like the ability to make your Bold font “slightly bolder, but not quite as bold as the Extra Bold”. In addition to working on the web, this font format will work in desktop applications, though applications will need to be updated to support it.
The work required to design a font family with many instances that work together like this will be no less work that it takes now to design a similar family now with all separate font files (contrary to what some might hope), aka there is no magic here. In fact it can take more design work and engineering to get them all into a single file in this new format, which I can tell you from personal experience in the last few day. But the benefit is that it can provide a tremendous added value of flexibility and compression to graphic designers, web designers, and other pro users. Currently the applications which support this new font format are very limited. But support is quickly being added, especially for web, and because the format was announced by Apple, Google, Microsoft, and Adobe I think it won't be long before more applications support this format.
More info about variable fonts:
Huge thanks to: Erik van Blokland for helping me through the process of generating a variable font, and for his work on MutatorMath and his related application Superpolator which is the best tool for interpolation in type design and has been supporting variation design since 2004. To Behdad Estabood and his team, and all FontTools contributors for making this new format possible, Adobe, Apple, Google & Microsoft for adopting the format (suppororting both PostScript and TrueType outlines), and Stephen Coles, Chris Lewis, Indra Kupferschmid, Bianca Berning, Nick Sherman, Tal Leming, Frederik Berlaen, David Berlow, Petr van Blokland, Just Van Rossum, David Jonathan Ross, Font Bureau, and Type Network.