When travelling and teaching last summer I bought a roll of Heat Press Batting Together™ to give it a try. The roll is 13.7 metres long (15 yards) and 3.8 cm (1½ inches) wide, enough for lots of joining. And it was SO easy to use.
The product reminds me of fusible tricot interfacing; it is a soft material with glue on the back side. Here are the simple steps:
1 - Cut a straight edge on the 2 pieces of batting you want to join.
2 - Place the edges together, but not overlapping, on your ironing surface.
3 - Cut a piece of 'tape' the length of the btting and place it glue side down with the batting edges in the middle of the tape.
4 - Press lightly with your iron.
It is the heat of your iron that makes the product work, not the weight of the iron. You just need to have the iron at the proper temperature. The package instructions include information for irons WITH Teflon plates and WITHOUT Teflon plates. I can't remember if mine is Teflon so I used the instructions for irons without. They recommend slightly under the WOOL setting for cotton and cotton blend battings. The first batting I tried was Hobbs Heirloom which is an 80/20 blend (80% cotton/20% thin polyester). The product worked just as it said it would and my two pieces of batting were now one useable piece.
The product made a white area where the pieces were joined so I wondered if this would affect a quilt made with white fabric. I set up a small sample and did some free-motion stitching over the area to see if the tape would affect my stitching and whether the white tape would show through. I had no problem stitching and there is no shadowing.
I also tried 100% polyester batting, this time Hobbs Polydown. I used the recommended setting (synthetic) and just skimmed the iron over the tape. The glue melted easily and the product did not make the batting stiff.
The shop owner where I bought the Heat Press told me that she has used it with both Quilters Dream cotton and Legacy 100% wool batting and it worked well for both types. So, if you have small bits of batting lying around get some Heat Press tape and make a larger piece for your next project.