Randomly wandering through blogs I came across someone who was showing this nifty idea. I was so taken by it I had to have a go at making one. Take the end off an old craft knife and remove the blade. These are cheap £ shop type. I found it works best if the material is wider so that the folds overlap or at least meet in the middle. Simply cut a point on the short end of the material, fold in 3 and ease the pointed end through the slot where the knife blade would have come out and ease the fabric down the length of the blade slot and then slowly pull the material at the pointed end where the blade would have emerged. The sides should fold in along the length of the blade slot and come out folded over neatly ready for ironing flat. On the blog (or you tube even) where I saw it originally she used a pair of hair straighteners ! The narrow knife was difficult to get the point of material through the end to start with so I made a puller with a loop of thread.
So apologies to who ever posted this originally but I do think its a great idea, well done and thank you for sharing.