Fusible Lining is an amazing way to give fabric structure and increase stability, as well as prevent it from stretching too much and providing a soft hand feel (especially great for quilting cotton!). Easy, fusible lining can be used on projects ranging from clothing and bags to cushions - I have even used it on pencil cases that would otherwise disassemble!
Fusible woven interfacing (FWI) is just fabric with warp and weft threads interwoven together that has an adhesive surface on one side that sticks it to other fabrics when ironed on. There are various weights of fusible woven interfacing available but medium weight should work best as it's the least thick or bulky compared to its competitors. You can find FWI at most fabric stores or online (here's where I get mine).
Fusible interlining comes in many varieties, from synthetic stretch fabrics like polyester or nylon to natural fibers like cotton or wool for natural fiber woven or knitted fabric projects. Furthermore, fusible interlining is often divided up according to what garment it will be used on; for instance, shirts require washable interlinings that have limited shrinkage and elasticity if intended as washable interlinings.
Factory pre-sample testing determines which fabric and fusible interlining is most suited for each garment through temperature, time, and pressure testing of adhesive powder particles from fusible lining combined with fabric yarn fibers to form a bond.
Finding the appropriate fabric or interfacing can be a difficult decision, as this choice will have a dramatic impact on both its appearance and feel. To avoid wasting both your time and money on something unsuitable for your project, it's worth conducting some research as well as studying examples of garments made using those chosen materials.
Before using fusible interfacing, first make sure that it has been pre-washed as directed (woven interfacing does not tend to shrink), with its adhesive side facing downward and secured to your fabric by stitching or pressing with an iron (the glue may stick directly onto your ironing board if not). Be sure to follow manufacturer directions when ironing directly on top.