I always use the same thread in the bobbin as the top, but to be honest it never occurred to me to use a lighter thread in the bobbin. I will have to try that. :) But I've never used 28 weight before...only 40 or 50 weight cotton. How thick would that be even? It makes me think of thread you'd use for bobbin work or something. I'd love for you to experiment and post some pictures of your results. :)