I am piecing a back for my latest finished top. I know how long and how wide. I just can't find which way to press the seams. Opened or closed? It is a very basic 8" finished strip. I will be machine quilting.

I always press the seam open on my backs, keeps seams laying flat and even.

if you are concerned about bulk in the seam areas pressing them open will help keep it to a minimum. pressing to one side would add an extra layer at each seam which may or may not be a factor when quilting. i think it is still personal choice and makes more difference if you are hand quilting...you want to reduce bulk, machine quilting doesn't really make that big of a difference. for backings i almost always press the seams open, i'm a long-armer and it helps the backing to roll evenly when loaded.

Thanks