The most common basket confusion, especially on Breville machines, is single-wall vs dual-wall — also called non-pressurized vs pressurized. They look almost identical from the top and are the same diameter, so they're easy to mix up, but they do opposite things. This is which is which, which you want, and which baskets in our database are each.
A dual-wall basket has two floors: the holes you see, then a second wall underneath with a single tiny pinhole. That pinhole holds coffee back and builds pressure artificially, so you get a thick, crema-topped shot even with pre-ground or stale coffee, a cheap grinder, or a sloppy tamp. The crema is a bit foamy and fades fast, but for convenience it's very forgiving. These ship with most machines as the "easy" option, and it's what most people should start on.
A single-wall basket has one perforated floor — dozens or hundreds of holes and nothing behind them. The puck itself provides all the resistance, so the shot is only as good as your grind, distribution and tamp. Get those right and you get proper, long-lasting crema and far better flavour clarity; get them wrong and it gushes or chokes. This is what you move to once you have a decent grinder and want to actually dial in espresso. Precision baskets (VST, IMS) are all single-wall.
Both must match your machine's size — a basket doesn't cross portafilter sizes (see portafilter sizes explained).
Each basket's wall type comes from the manufacturer's own listing, quoted on its entry. See how we verify compatibility.