I have some jeans thread I use to hem my jeans (I am very short) and it works just fine in my Janome 6600. I use a longer stitch and a walking foot...no problems. I see no issues with using the thread as long as you use a bigger needle (16-18) and a longer stitch. It will give great definition for straight line quilting, but probably not suitable for SITD or FMQ. I think it would be great for a quilt made with denim!