Invisible thread.
 

I have just invisible threaded my applique pieces before hand stitching patterns round the shape.

Having been scrunching my fabric in my hand as I embroider I have creases on the block. Could you please advice me as I want to iron them out, what temperature is best do ineed to cover? Will the invisible thread melt onto my iron and fabric.
DOTTYMO

which type of invisible thread did you use?

Rayon Madeira says it is embroidery thread but I am Using in the sewing machines

I have some wrinkle release spray - you just spray it on and then smooth the fabric with your hands and the wrinkles vanish. Maybe something like that would work?

I have pressed fabric that I used monofilament thread on with no problems, I can't even remember being careful but perhaps just stay away from where the thread is just make sure your iron isn't on high temperature.

I've had no problems with monofilament. If it's nylon, you will not be able to iron it.

Take some strands of the thread to your ironing board and use a hot iron to press them onto a scrap of fabric. I have done this with nylon monofilament to test if it would melt; it was fine. If your thread survives this test, you can safely iron your appliques.

Thank you for all your replies. Never thought about testing it. Dumb or what?