Hi, The opaque I use is Jetwear Dark and also Jetwear II double green line which I buy from T-shirt Supplies.com. He also has an e-bay site with good prices. The other thing you need to know about opaque is when printing do not mirror image the design and after printing it needs to be trimmed or you will have a white background in your design. There are instructions on the package on how to separate the backing from the front before trimming and then use scissors or commercial cutter to trim around the design, place right side up and cover with paper included and heat press, let cool and remove paper. If you use good ink and "best" for ink settings on the printer, you will get good results with opaque for dark shirts. The only way to avoid the polymer on light color shirts is to trim as close as you can to the design and again if you have a cutter then you can trim these as well and no polymer will show. I use a Craft Robo and can trace designs and then cut them so it's a lot easier to do t-shirts.