I straightened my closure using the Remington Keratin Therapy Pro S8590 Ceramic Straighteners I mentioned here.
It straightened really well as you can see below. Before:
Of course I used heat protectant. The closure is a 14 inch body wave closure. If you remember here, I stated this is Virgin Brazilian hair I am wearing to test before selling it- I love it so far and it curls so well.
How I Made My Wig: