I use well washed smooth surface cotton pot holders as the ironing surface for little pieces - like triangles or pieces of applique because it is easier to spin it under the iron, than crank the iron around at wonky angles. I put them on a bigger piece of masonite, so if the hot iron gets off the edge of the potholder, it won't hurt anything.
I spin the potholder and the masonite together. The masonite is smooth side down, rough side is up - against the bottom of the potholder and holds it from slipping.