Quick answer
For a typical Canadian interior wall (smooth or light orange peel): a 9-inch roller frame and a 3/8 inch nap cover. Bump to 1/2 or 3/4 inch nap only if the wall is obviously textured. Mini rollers are for doors and cabinets, not whole rooms.
Frame vs cover — spend on the cover
A $12 frame and $8 covers beats a $4 foam kit that sheds. Foam rollers are for cabinets and ultra-smooth doors, not drywall.
- Frame: metal cage that locks so the cover cannot slip sideways
- Cover: the fabric that holds paint and sets texture — this is what you replace
- Extension pole: screws into the handle; buy one, your shoulders will thank you
Nap size cheat sheet
If you are not sure, start at 3/8″. Too-long nap on smooth walls leaves an orange-peel look you did not want. Too-short nap on texture misses the valleys and looks starved.
- 1/4″ (very short) — cabinets, doors, ultra-smooth trim panels
- 3/8″ — most interior walls and ceilings on newish drywall
- 1/2″ — light knockdown or heavier orange peel
- 3/4″+ — heavy texture, masonry, stucco-style interiors
How to load and roll (so you do not get stripes)
Dip, then roll off excess on the tray ramp until the cover is even, not dripping. Start in the middle of the wall and roll a W or M, then fill in. Overlap each pass about a third. Keep a wet edge: finish a wall before you stop.
When the cover starts to mat or spit fuzz, swap it. One spare cover per colour is cheaper than sanding bits out of a dried wall. Calculate gallons first with the how much paint calculator so you are not changing covers mid-colour with an empty can.