Choose the Right Interfacing
Use interfacing between layers of fabric to add body and stability. The many types of interfacing can make it challenging to choose the best one for your project. Here are four popular types and their most common uses.
Best for bags and home decor projects. Foam interfacing provides a thick, slightly stiff foundation that often takes the place of batting in bag and home decor projects, such as storage baskets. When sewn inside bags, pouches, or zippered cases, it can help protect fragile items.
Best for bag bottoms, hat brims, and baskets. As the stiffest interfacing, heavyweight interfacing gives hat brims and bag bottoms their stability. It comes in one-sided or two-sided fusible variations, or without fusible (look for "sew in" on the packaging). Avoid using fusible on delicate fabrics that can't be ironed. It tends to be nonwoven, so you can cut it without worrying about bias edges.
Best for bag linings. Fleece provides a soft lining that is good for bags and cases. It is available in different weights and with or without fusible. Try to match the weight of the fusible fleece to the fabrics in your project.
Best for appliqué, garments, and T-shirt quilts. Lightweight interfacing adds stability without adding much bulk and helps keep bias edges from warping. It is often used in collars of garments and T-shirt quilts. It comes in different weights, with and without fusible, and in woven and knit varieties. Try to match the weight and degree of stretch of the lightweight interfacing to the fabrics in your project.