Each person has their own preferences. There are those who prefer fusible interlinings and others who prefer non-fusible ones. I personally prefer non-fusible interlinings. Later I will tell some reasons that make me prefer this option but first of all I want to clarify that neither option is better than the other as long as they are used correctly.
When you go to a store and ask for an adhesive interlining the answer is clear and you will be presented with several options with different thicknesses. However, there is no specific fabric that is considered a non-fusible interfacing (except for the specific one for tailoring). A non-fusible interlining is any fabric that has the type of body you want for your garment. Common choices are usually poplin or cotton plain weave, cotton twill or even organza. And yes, these are fabrics that you will have used many times as the outer fabric of your garment, such as blouses, jackets…
How is a non-fusible interlining used?
The methodology I use is to cut the outer fabric piece first and place it on top of the interlining fabric (you can also do it the other way around). The interlining has to be in contact with the inner side of the fabric.
The pieces should be placed on a flat surface so that no wrinkles are created between the two fabrics. Of course there are advanced exceptions when we want to obtain specific results but these are general steps for a basic interfacing.
I baste the two pieces together carefully with the outline so that they are joined together and act as a single layer of fabric.
Some people pin the two layers of fabric together or machine stitch along the contour of the pieces. I don’t like these methods even though they are faster, but these are just my preferences.
Can I only use one type of interlining at a time?
You can use fusible interlining and non-fusible interlining at the same time. As you can see in the picture I have outlined my taffeta pieces with strips of fusible interfacing to prevent the fabric from fraying. I then used non-fusible interfacing to give the fabric more body.
Some very light fabrics may require fusible interlining to give them a stabilized surface before using another type of interlining, e.g. crepe.
Once the piece and the interlining are basted we will cut the interlining following the shape of the piece. Now you have your pieces ready for the sewing phase!