Interfacing is a product you can use to stiffen fabrics and add stability and shape to things like collars and cuffs. It can add strength to button holes and can also help fabric hold the shape into which it was sewn. A multitude of interfacings are available on the market today, each one having its own manufacturer's instructions. But in general terms, there are two interfacing types: sew-in and fusible. Each has its place in sewing projects, and many patterns tell you exactly which one to use. But you can also experiment to get the results you are looking for and the stiffness your require.
Choose the appropriate interfacing for your project. Select an interfacing that is lighter than your project fabric and take into consideration the type of fabric care the finished garment will require. Be sure the interfacing works with the way you will be draping your fabric.
Pre-shrink your interfacing. Treat your fabric and interfacing by washing them in the manner the garment will be cared for once the project is completed, or follow the manufacturer's instructions on how to pretreat your fabric and interfacing.
Cut your interfacing to the same dimensions as the piece of fabric it will be stiffening. Remember that some interfacings have grains similar to other fabrics and should be aligned with your fabric grain.
Test your interfacing and fabric combination before attempting your final project.
Steam shrink your interfacing by placing the hot steaming iron 1 to 2 inches above the interfacing without touching it. Steam it for 5 seconds.
Pin the interfacing in place to the wrong side of your fabric so that all of the edges are aligned.
Use your sewing machine and a contrasting thread colour to attach your interfacing to the fabric. The contrasting colour makes it easier for you to locate the basting stitches and remove them later. Use a long straight stitch to baste your fabrics together 1/2 inch from the outer edge. Do not backstitch to lock in your stitches. You may remove the basting stitches once your project is complete.
Trim the interfacing to remove any that protrudes into the seam allowance. This will reduce bulk in your seams. This is an important step for thicker fabrics but may not be necessary when you are using thin fabrics.
Continue sewing your project as normal.
Lay your interfacing on the wrong side of your fabric so that all of the edges are aligned. Make sure the adhesive side of the interfacing is touching your fabric. Locate the adhesive side by looking for the tiny glue dots on the interfacing.
Reduce bulk at your seams by trimming the seam allowance from the interfacing. Make sure the interfacing is aligned properly in the centre of your pattern piece. If the interfacing only covers a portion of your fabric piece, trim the edge with pinking shears to avoid a visible line created by the interfacing.
Steam shrink your interfacing by placing the hot steaming iron 1 to 2 inches above the interfacing, without touching it, for 5 seconds.
Baste your interfacing to your fabric by gently touching the tip of your hot iron to a couple of places on the fabric. This will hold the interfacing in place and prevent it from slipping while you iron it on.
Lay a damp, white, colour-fast cloth over your project and hold the iron in one place for 10-15 seconds. Lift the iron and re-dampen the white cloth with your spray bottle. Move the cloth to the next area you are adhering and iron for 10-15 seconds. Continue in this manner until the entire piece of interfacing is ironed on. Allow your piece to cool completely before moving it. Continue sewing your project as normal.
Test your interfacing by using a scrap piece of interfacing and a scrap piece of your fabric to make sure the method of adhesion you are using is compatible for both pieces.