Variable fonts is an OpenType font specification that puts different variations of a typeface into one single file instead of multiple font files for every variation that you may need. With a standard font, your visitors have to download multiple files which leads to more HTTP requests and data to their browsers. With a variable font, the file size may be about the same but you’ll have access to a much wider range of styles than currently available. For example, a font like Roboto has twelve font files which includes twelve variants. The variable font has one file and unlimited variants.
Can I Use It?
Not all browsers and operating systems support variable fonts. For example, Linux OSes need to download the latest Linux Freetype version and Macs need to use a Mac High Sierra (10.14) and Mojave.
For non-supporting browsers, you can use CSS Feature Queries to determine if it should load a standard font instead.
Why use Variable Fonts?
You can use a single font file that provides you with a wide range of widths, weights, slants and more. With less font files to download, your visitors don’t have as much to download. With a variable font, you have greater flexibility on how your text displays. You can use a wider variety of font variants to create certain affects that help define your style and voice. With most major browsers supporting this font type, you can start to use them in your next project.