I never save my selvages. They're just not appealing to me when I look at them lying there on my sewing table.
To keep my mug rugs flat, I do 2 things. First, I use a low loft batting, the same that I would use for making placemats, which I always have on hand. I usually buy Poly-fil brand for this, but I like Mountain Mist as well, depending on where I'm shopping when I need to buy it. Second, I rarely bind my mug rugs. I usually sew them pillowcase style and then turn them right side out and sew around the edge.
Oh, I almost forgot what brought me here to begin with! I got this week's special from Joann this morning & they've got FQ's for $.99 each, in store only (online, $1.49, but they only have a few online.) Hmm, I think I need to go to Columbus next weekend!
