Most flat-bottom drippers use a wave filter: a pleated cup whose ridges hold the paper away from the dripper wall. Those ridges also leave channels where water can run down the side instead of through the coffee. A flat filter removes them. Once wet, the smooth paper sits against the wall with no folds or relief, so the water has to pass through the bed. The result is a more intense, controlled extraction that brings out sweetness and body while keeping the cup well defined.

Why the paper matters more in this format

Take away the bypass channels and the drawdown depends almost entirely on how permeable the paper is. A dense paper in a flat format can choke the brew, which is why flat filters tend to be made from fast papers. HIFLUX’s High Fast paper uses regenerated lyocell fibre in a three-dimensional structure, which HIFLUX state flows up to 42% faster than conventional paper. The pore size is designed to let particles below roughly 20 micrometres through, adding texture to the cup, and the smooth, continuous lyocell threads give oils less surface to cling to than plain pulp, so more of the aromatic oils reach the cup.

Dialling it in

Because a flat filter hugs the dripper, its flow rate depends more on the shape of the dripper than a wave filter’s does, so expect to adjust your grind when you move between drippers. Timing the drawdown on a scale such as the BOOKOO Themis Ultra makes those changes easy to track, and a pour-over grinder with fine adjustment, such as the 1Zpresso ZP6 Special, lets you move in small steps. Rinse each filter with about 100 g of hot water before brewing; this also seats the paper against the wall and preheats the dripper.

Fit

HIFLUX have not published a list of compatible drippers for the 165 mm flat circle. It is made for flat-bottom drippers, so check the base and wall of yours before buying. If you would rather stay with a pleated filter, the HIFLUX High Fast Wave filters use the same paper in the standard 155 and 185 wave sizes.

Specifications

What’s in the box

• 50 × HIFLUX HIGH FAST Flat Circle 165 filters