What is "fusable interfacing" and who uses it to make kilts?

[Paul Henry]

fusible interfacing can be useful , but you will find very few professional tailors making quality garments who use it much or often.It does have a place of course, and it can be useful, but you will find that a hand stitched interfacing allows greater shaping, or adding different layers and weights, and actually it's often easier to hand stitch smaller pieces than using the iron on stuff.
Realistically it is a shortcut, and whilst the "heat glue" has imporved over the years , it can delaminate over time or washing.
If I am spending a relatively large amount of money on fabric, I'm going to making the garment in the best way possible, and that still remains using non fusible interlining

[Dixiecat]

Realistically it is a shortcut, and whilst the "heat glue" has imporved over the years , it can delaminate over time or washing

This can happen, yes, but doesn't matter a hoot. Consider that sew-in interfacing is just a layer of cloth. The only difference between it and a fusible is the heat sensitive resin. As long as the fusible was applied correctly, and finished properly (no exposed edges), I have experienced no issues on having a fusible delaminate.

What I have had issues with, is the non-woven 'fabric' that some interfacings are made from. With heavy wear and repeated washings, it can sometimes fall apart or 'whisker' itself to nothingness. I always try to go with woven fusibles over non-woven.