How to make iron-on letters?

Does anyone know what I would need to be able to make these? I'm assuming just cotton fabric would be OK, but what is the iron-on stuff called?

Yes cotton is ideal in my experience and I use Easy Fix - Double Sided Iron-on Adhesive which you can get in sheets or a roll of stuff.

Thank you! I have been trawling the internet hoping that I might have been able to buy them to save me the hassle but they are all really expensive. Can I just get that at Spotlight?

vlisofix is another brand of the sticky stuff...both available from spotlight....vlisofix is a tad more exxy but tends to be longer wearing if you are not going to stitch the letters as well..... definitely use cotton as you need quite a hot iron to activate the sticky and a polyester fabric may melt a bit

vlisofix is what I was going to suggest too, but would cotton fray too much if it wasn't edged?

I have iron on stuff I got at Big W for about $10 a packet. Iron it to the back of the material cut out your shapes, peel off the backing then iron onto your project