I bought a few last week and did tests. I wrote on 3 different types of fabrics. I let the ink set for about 3 hours then pressed with a very warm iron. I found I needed to use a very hot iron. So if your fabric cannot withstand a hot iron, another "heat" source is needed. I then took the fabrics and put them in the freezer. The ink did return, but not as bright. I then washed the fabrics with warm water and detergent. I dried one sample in the dryer and the other by laying out the fabric. I did not try washing in cold water(oops, I forgot), so I cannot give a honest answer if the ink comes out in cold water. After both fabrics where dry, I put them back in the freezer to see if the ink returns.
i could not see any residual color from the pens. The satin had a faint mark, almost as if the pen point left a scar. The cotton and the poly-cotton both were clear.
I would absolutely test your fabrics first. But for myself, I was pleased with the results.