Believe it or not, there are coffee cups that are neither porcelain nor ceramic. And we're not talking about paper coffee cups. People have a tendency to put their caffeine in just about anything they can get a hold of. There are some who even swear up and down that their coffee tastes different coming from glass coffee cups than a more traditional coffee cup. However, there are a few other reasons why someone might decide glass coffee cups are better than porcelain or ceramic.
Aesthetics
Some folks like to see what they're drinking, and most coffee cups don't allow for that. If you can't see it, how can you be sure your cafe mocha contains the correct portion of cream, and that cappuccino the right amount of milk foam? When it comes to coffee, not everyone "gets it", so coffee shops might make use of glass coffee cups to let their customers know that they're getting what they're paying for.
Durability
Yes, glass is known to be breakable, but consider the alternatives when it comes to dishware. As with porcelain and ceramic, thickness and quality are king. Both porcelain and ceramic will chip far easier than a glass coffee cup, as well. Besides, even if you drop a glass coffee cup, it's very unlikely that it will break, unless you drop it on stone, concrete, or something similarly hard, and even then a porcelain or ceramic cup would've broken just as easily.
Ability To Keep Coffee Warm
There's no particular coffee cup material, be it ceramic or porcelain, that will keep your coffee warm, regardless of what some say. Heat does not transfer well through those materials, though, making them ideal for use as coffee cups. The goal isn't so much to retain heat as it is to provide a handle that's touchable by human hands. Generally speaking, glass does transfer heat a little easier, but glass coffee cups usually are made in a way that make them even more heat resistant than your standard cup. Of course, none of these will keep heat in like plastic or aluminum insulated mugs, or even lidded disposable coffee cups.
Price
Glass coffee cups are much more elegant looking than their more traditional cousins, so many people assume they're pricey. However, glass coffee cups are about as affordable as any quality coffee cup, regardless of the material. There are even glass espresso coffee cups available, complete with little glass saucers. Finding glass coffee cups can sometimes be a challenge, but most larger department stores will carry them, and you can always find an enormous selection online.
Want to learn more about glass coffee cups? Check out Great Coffee Cups.