I've see the same lids every day but I never really thought about their construction. There is an indent in a "Solo Travel Lid" for coffee cups that is just above the hole that you drink the coffee from.
You can see the crescent shaped indent in the image. What is it for? Does it somehow increase fluid flow? Is it just a good spot for your upper lip? If so, why is there not a matching one for the nose? I tried googling this but I got no answer.
From the "Solo Traveler" patent:
A more specific object of the present invention is to provide a lid having an opening formed therethrough to enable drinking, and having a recess formed in the lid adjacent the opening to accommodate the upper lip of one drinking from the cup
This is also illustrated in the patent diagrams.
I came across this interesting article on the history, use, design, and styles of disposable lids. The Solo Traveler is prominently featured for its excellent aesthetics and design . The article reiterates that:
the Solo Traveler lid was designed to accommodate the nose and lip of a drinker. In accomplishing this design goal, the necessary height of the lid made it useful for foam-topped gourmet coffees.
Additionally, when upright, the recess acts as a reservoir (complete with drainhole) to catch drips/spills/splashes that might otherwise run down the cup and create the infamous coffee stain ring.
