Those little tiny plastic bags they sell at Hobby Lobby. They are for Jewelry makers primarily, i think. They are just right size for a spool of thread. No matter how you store them they stay dust free and don't get unwound and tangled. I throw them into baskets. One for black and white, one for brown,tan,gray (gray is every quilters favorite color), one for red,pink,purple,yellow,warm colors, and one for cool colors blues and greens.