I don't like the idea of having to fold it and unfold it every day, so my current inclination is to just leave the 20" width unfolded and roll it tight, wrap a thinlight pad around it and either pack the result inside my pack vertically or put the result in a garbage bag with rubber bands and strap it outside my pack.

If I change my mind, I can get the Neo-Air size regular in a gallon ziplock folded --- I think in thirds, I don't remember.