If the interfacing melted, you might have a wash away stabilizer. There are approximately 8,972 different types and weights of interfacing and stabilizers, made by many different companies. Interfacing stays in your completed project to add support. It can be sewn in or ironed on. The iron on stuff has heat activated adhesive on one or both sides, the sew in versions don't. Stabilizers are meant to be temporary, firming up the fabric so embellishments such as embroidery can be added, then they wash away or tear away. At many stores, everything is shelved together so you have to read the labels carefully & purchase the correct weight and type for your project. The pattern should tell you specifically what you need. There normally is a piece of paper that comes with your interfacing or stabilizer that gives you instructions on how to handle. Be sure and keep that and follow the instructions carefully, for instance it will tell you the temperature of your iron and if you need steam or not.