Miele Guard L1 bags and filters
TU dust bags, an SF-HA 50 HEPA filter and an SF-AA 50 exhaust filter. Every version listed below fits.
Every version in the "Also covers" list takes the same parts.
Dust bags
HEPA filters
Exhaust filters
Finding the model number
It's worth a look at the rating plate first, because names get reused across generations. Data plate is underneath the vacuum cleaner.
When to change them
Change the bag when the marker in the bag change indicator turns red (fine dust can trigger it early; hair and fluff can fill the bag before it shows). Each 4-bag pack includes a fresh AirClean exhaust filter; Miele says the exhaust filter needs changing about once a year on average. (source)
A bag that's only half full can still be done for: fine dust blocks the pores first, which is why the indicator can go red early after a lot of plaster or fireplace dust.
Seeing a full warning on a fresh bag usually points to a blockage in the hose or floorhead. Check there before blaming the bag.
Washable filters go back in bone dry or not at all. A damp one smells, and on some machines it can let the motor pull moisture through.
Quick answers
If I've got a Miele Guard L1, which dust bag do I need?
TU, which Miele sells in 2 different packs.
Which HEPA filters fit the Miele Guard L1?
SF-HA 50, or any of the other 2 Miele versions listed above.
Which exhaust filters fit the Miele Guard L1?
SF-AA 50, or any of the other 3 Miele versions listed above.