kengr

Cat Faye says: "I would put a layer of ultralightweight fuiseable interfacing under the sleeve fabric so it doesn't fold into itself. I'm thinking the kind you iron on to the fabric."

Fuiseable means that it adheres to fabric when heated and becomes a part of the fabric.

Here's a link: https://www.pellonprojects.com/products/p44-plf-fusible-interfacing/