I modified the wonderful design by Erik Cederberg to fit on the Prusa Mini bed. This is a US model designed for 8.5x11" ish sheets. I use Avery 16741 as they are thick and nice plus you can get them at local staples/walmart/etc. Approx 70 have been handed out with no complaints. I like this design because elastic is not needed. Elastic is the hardest thing to find right now. The wearer can use a rubber band or hair tie to make the fit even better but it's not required.
For more details please see 3DPN video. I have linked the original source for more information and to get full size versions.
The author hasn't provided the model origin yet.