There are a few cup holder expanders for vehicles out there, but I wanted to include some details from several of the versions I saw online. This one includes smoother edges all around, and the onside will fit a can, such as a 12oz Coke or a Monster can. The upper portion is designed to fit my Simple Modern 32oz water bottle. Hydroflask and Yeti would likely would as well. The bottom fits comfortably in my 2021 Silverado cup holder.
Update - I upgraded the file to filet the inner edge at the upper wall. This reinforces that connection to the base of the cup more. I also adjusted the print to .2mm/layer to give stronger layers. Lastly, I suggest printing in PETG as opposed to PLA.
The author marked this model as their own original creation.