I sewed these flex frame pouches using Tilda fabric for the exterior and lining of the pouch. I used 3.94 inch metal flex bands for the 'snap' mechanism which inserts into the casing that is created when sewing.
The finished size is approximately 4 x 4.5 inches.
I was inspired to sew these after seeing a simple technique that is demonstrated on 'upacoHM' to create these pouches.