Polyamide is the generic name for all long-chain fiber-forming polyamides with recurring amide groups. Polyamides (Nylon) comprise the largest family of engineering plastics with a very wide range of applications. Polyamides are often formed into fibers and are used for monofilaments and yarns (IE jacket material)
If its a Mix of polyamide/cotton then I wouldn’t have any problems with putting nylo flex, or such like onto it.
Normal garment vinyl is slightly thicker and more likely to have less give in it and not press so far into the garment.
Its a little like comparing cast vinyl to calendered vinyl, IE easier to work into the garment, easier to work into a recess etc.
Cut a little nylo flex and press onto the inside of the jacket where the zip goes or inside of a pocket where the same material that is on the outside is exposed but cant be seen, if it sticks all well and good just spray on some transfer remover spray and take it off, then carry on and do the job.
Im assuming you have the spray to hand, as its a necessity in any garment printers workshop.
Thats all I do anyway, press a small bit onto a part of the garment that isn’t visible from the outside if its ok press it, & remove the odd test bit with the spray.
if not use a different material, but nylo flex sounds perfect for this one.