To keep a shirt collar in its beautiful shape, a core must be inserted into the collar to give the fabric stiffness. There are two methods for doing this: fusible interfacing and non-fusible interfacing, and it is said that in Japan, 90% of shirts use fusible interfacing.
Fusible interfacing is a material that is semi-permanently bonded to the fabric using adhesive. While this has the advantage of making care easier, it also makes the collar stiffer, which takes away from the original texture of the fabric.
This is why Shuttle notes shirts use plush interlining.
The soft texture of traditional plush interlining cannot be achieved with fusible interlining, and the comfort it provides around the neck is unmatched.
The plush interlining is an inefficient sewing method that can only be made in factories with high sewing skills. However, we use it because we want to create a top-notch product not only in terms of fabric but also in terms of sewing.