Iron-on patches
There are many kinds of iron-on in the market; different compositions have different sticking capability. Iron-on can only be used for 100% cotton fabric, T/C, T/R, wood, metal and so on. It's not good for fabric that contains polyester upwards of 50%, and also cannot be attached on PU, PVC, corium, raincoats, reflective fabric etc. Below are instructions:

IRON-ON INSTRUCTIONS FOR EMBROIDERED PATCHES
(Household Application)

CAUTION: The following instructions are for ironing your patch onto a cotton garment. For other fabrics or bulkier garments, follow the manufacturers recommended heat settings. To assure a good bond on hard to bond fabrics steps 5 and 6 may be repeated 2 or 3 times.

1. Place a cloth (t-shirt, pillow case, or similar thin cotton type fabric) on a hard, non-heat,
sensitive, sturdy surface (kitchen counter, desk, cutting board, hard cover book, etc.).

2. Position area of garment where patch is to be attached on cloth, face up.

3. Position patch.

4. Cover patch with a pressing cloth (t-shirt, pillow case, or similar thin cotton type fabric).

5. Apply hot household iron (hottest setting), with as much pressure as you can apply for 60 seconds.

6. Turn garment over and repeat steps 4 and 5 from the reverse side. Without allowing garment to cool move pressing cloth to a new position (to prevent scorching), and repeat step 5 again.

7. Allow patch and garment to cool completely before handling.

NOTE: Wash at moderate temperature. In the rare case a patch loosens, it can be re-attached by repeating steps 4 through 7.