Single-wall and double-wall describe how many layers sit between the coffee and the cup. Simple. But the count changes how the basket behaves, so it's worth knowing which one you're holding before you buy a spare or change your grind.
What each term means
A single-wall basket is one metal cup with holes covering the entire base1. Coffee sits on those holes, and the liquid drops straight out.
A double-wall basket is "a metal espresso filter with an inner and outer wall"1. The inner wall has many holes at the bottom. The outer wall has a single, small hole at the base1.
Makers and writers often use other names for the same two designs. Double-wall is the pressurised type, and single-wall is the non-pressurised type1. The pressurised vs unpressurised page covers that naming in more detail.
How the layers change the shot
With a double wall, water has to get through the inner holes and then squeeze out of the outer wall's small hole. One maker says this design is made to "intentionally slow the water" during extraction2.
A single wall is different. Nothing extra slows the water, and the coffee puck does the resisting1.
Which coffee each is meant for
Manuals usually tie each wall type to a kind of coffee. One maker's manual gives this guidance:
- Single-wall baskets are for freshly ground whole beans. They let you experiment with grind, dose and tamp "to create a more balanced espresso"3.
- Dual-wall baskets are for pre-ground coffee. The manual says they regulate the pressure and help the extraction, whatever the freshness3.
Tamp means pressing the grounds down into the basket. Dose means the amount of ground coffee you put in.
That's one maker's advice for its own machine. A different Breville model's product text says both its pressurised and its non-pressurised filters suit pre-ground vacuum-packed espresso and fresh ground beans2. So follow your own manual rather than assuming one rule applies everywhere.
Side by side
| Single wall | Double wall | |
|---|---|---|
| Layers | One cup1 | Inner cup inside an outer cup1 |
| Base | Holes across the base1 | Many holes inside, one small hole outside1 |
| Water flow | No extra slowing2 | Deliberately slowed2 |
| Maker's suggested coffee (one manual) | Freshly ground beans3 | Pre-ground coffee3 |
Picking between them
Don't force the other type in without checking. Some machines are only meant to use one1.
When you can't tell what you have, begin by working out what's in your portafilter.
A word on terms
You'll see the same basket described in several ways. A shop or manual might say dual-wall, double-walled or pressurised. Another might say single-wall, non-pressurised or unpressurised. They're pairs of names for the two designs above1.
Don't mix up "double-wall" with "double basket". The first is about layers. The second is about size, and it has its own page: single and double baskets. A basket can be a double size and a single wall, so treat the two ideas separately.
Where the facts come from
- Pressurized vs. non-pressurized baskets, Breville
- Breville BES830XL product resources, Seattle Coffee Gear (reproducing the maker's product text)
- Breville BES870XL manual, selecting a filter basket, Breville (via ManualsOnline)
More on baskets
What a Portafilter Basket DoesWhat the basket inside an espresso portafilter is for, and how its design shapes the way water moves through the coffee.
Pressurised vs Unpressurised BasketsHow pressurised and unpressurised espresso baskets differ, who each type suits, and how to tell which one your machine uses.
Basket Sizes and Dose RangeHow an espresso basket's size, its stated dose range and the coffee you put in relate, using a maker's own manual as the guide.