This was designed so that you can rip out the existing plastic shell leaving just the leather soft case.
Then use double-sided sticky tape to adhere the print to the inside of the soft case.
For bonus points, you may want to stick some old material to the inside to protect the glasses, or just push a screen cleaning cloth in first to prevent scratches.
The author remixed this model.
Based on boredredditor47's original model which was designed to work WITH the existing plastic insert, this remix replaces it entirely and includes a middle section that supports the bridge of the glasses (as well as providing additional rigidity.
This model is wider than the original to accommodate full-width Ray Ban Sunglasses, and has been extended vertically to take up the entire space of the soft case with no standard shell.