This is the tenth iteration of coasters I've designed, and the best by far. It is designed with several properties I thought were important:

• It takes condensation off of cups / bottles / etc. as it drips down, keeping them from dripping on you too much on hot and humid days. (Mostly. It's not perfect.)
• It is easy to clean. Surfaces are mostly curved so it's not hard to get a sponge into them, and it's easy to wash if it gets dirty. (Hand wash only! Don't melt plastic in your dishwasher.)
• It stacks, so you can have a number of them ready for use without taking up a bunch of space.
• It's easy to pick up, with a rounded top lip, and has few sharp edges so it's comfortable to use and move around.

I've been using these for almost a year now, and they work quite well. Printing with PLA (even extremely cheap stuff) seems to be fine: they don't seem to leak even after collecting a fair bit of condensation.

The MK3S+ can print three of these in a go with “Complete individual objects” turned on, which I'd recommend if you want several: if you try to do them all simultaneously, sometimes they can end up warping off the bed and ruining the print.

The corresponding FreeCAD file is included. Please do not sell this model without contacting me first.

Printing

• Rafts: no
• Supports: no
• Infill: 15% (less would likely be fine, but has little benefit for this piece)
• Perimeters: 2
• Layer height: 0.15mm (0.2mm could work, but the curves will be more jagged)
• Material: PLA (others would likely work)
• Other: I would generally recommend turning on the expert setting “Avoid crossing perimeters”, as it will keep the coaster slightly neater by reducing stringing artifacts from movements between the bars, and has effectively no print time impact.