Overview:

We had a couple straps break on our kids’ flippers, so I modeled this one as a replacement.  They are more comfortable than I expected but the softness and feel will be determined by the filament you use.

I’ve included my Fusion 360 file and step file, so you can customize it for the size of your flippers or anything else that needs a similar style strap.

Printing:

I recommend printing in TPU.  No supports are required if printed in the orientation shown.