Which ever side you want to use would be the right one. Just like many fleece fabrics, you can use which ever side you want, there is no right/wrong. Some have more of a sheen on one side, some the nap is different, but it still doesn't matter, if you don't like the sheen you can use the dull side, if you like one nap better, use that one. I've always paid for both sides of my fabrics and use the side that works best for my project, regardless of what kind of fabric it is