The spot in my office where I park my Ozark Trail insulated cup is under an A/C vent that is not always as clean as I'd like. I've been covering the cup with a tissue and rubber band when I leave for the day or weekend. Figuring it would be rather easy to do, I designed a cover for the lid that I could print. When I designed the object I figured on 100mm across the top of the cup (which I measured). When I printed it I found that it was a bit small. I reprinted it at 103% and it fit perfect. This is not a "snap-fit" cover. It simply sits on top of the existing lid to keep stuff out. Your mileage may vary.
I printed with a 4mm brim but that's your choice. I am using a Geeetech Prusai3 Pro C with Elmer's glue stick.
I thought about creating another print to personalize the top but thought I'd use my Brother Design-n-Cut vinyl cutter instead. I downloaded the decal image.
I needed to do a little sanding on the top edge (which was facing the print bed). I used supports so I had to clean that up a bit as well.