S Bags.
Hey Joe-
The type A, K, S and Z bags come in two different varitits. Regular and Allergen Filtration. The regular bags are green and one layer--much like the current type J bags for the old Constellations (and most of the other bags--type C, D, E, G, H, J, M, N, X). The Allergen Filtration bags are like the type Y bags for the Windtunnel--a thicker, more dense paper that holds 100% of dust mites and their eggs, and 99.9something % of ragweed and common grass pollens. The Allergen S bags used to come with the rubber seal, and that's what I have in my machine that is in the pictures (I was waiting on my bags from England). I had an older package of them. With keeping costs down, I'm sure, that's something they did away with pretty quickly I imagine. I've even purchased a few packages of bojack allergen filtration bags (don't tell anyone), and have not found any to have the latex/rubber seal.
There is also one step above the Allergen Filtration bags, which would be the HEPA filtration "Filtrete" bags by 3M. The only type of bags that are available as "Filtrete" so far are the type Y and Z (one bag that works in either type of machine). And that is what I imagine will be offered for the new Constellation...but am not 100% sure, because they could just put a HEPA filter before the motor, call it a day, and tell people to use the S bags.
~Fred