24 Ways is my favourite advent calendar and this year is not disappointing. There are back to back tutorials on Variable Fonts and I highly recommend you starting with the overview from Jason Pamental before following up with Mandy’s.
Everything you thought you knew about fonts just changed (for the better).
Typography has always been a keen interest of mine, long before we were able to use fonts on the web. And while we’ve had the ability to that now for ten years, we’ve always been constrained by balancing the number of fonts we want to use with the amount of data to be downloaded by the viewer. While good type and typography can bring huge benefits to design, readability, and overall experience—include too many fonts and you negatively impact performance and by extension, user experience. Three years ago, an evolution of the OpenType font format was introduced that changes things in some really remarkable ways.An excerpt from An Introduction to Variable Fonts