Insert for a HydroFlask Boot for containing an Apple AirTag. This model is two separate discs. Outer disc to be printed in a harder impact material, PLA, PTEG, ASA, ABS. As well as an Inner disc to be printed in a softer cushioning material TPU. 

2 perimeters
15% Infill

I find that the SainSmart TPU setting works quite well. 
I can also see a personalizing option added to the Outer Disc If you didn't want to use the AirTag.