The GN HyClean bags were described as "9-ply construction". At least in the brief time -- last three months -- I've used them.
At this point, I'm easily mixed up on the names HyClean, intensive Clean Plus, Air Clean. Worse, in some dealers I've been into, when pricing Miele vacs recently, I now realize they still have some stock of the evidently older (Intensive Clean?) bags. They would pull these bags out when asked 'how much are the bags?', and say something about 'there are five bags in this box and we sell three boxes for blah blah blah.' Those were the dealers I checked off my list of ones I wanted to deal with.
Vacuum history:
-- Electrolux 1205 (ran for 28 years, then it needed a new hose and replacement wand!);
-- Metropolitan Vacuum Cleaner "Vac N Go Hand Vac", 12V (auto power) mini canister x2
-- Miele LEO.