The newsletter they sent me said it's mercerized cotton.
http://en.wikipedia.org/wiki/Mercerized_cotton Wikipedia said this is a process of treating the fabric where it no longer shrinks and is what gives it it's sheen.
This treatment increases luster, strength, affinity to dye, resistance to mildew, and but also increases affinity to lint. Cotton with long staple fiber lengths responds best to mercerization. Mercerized thread is commonly used to produce fine crochet.
Sounds like it has it's uses but not in a sewing machine. What does everyone else think?