Introducing The Perme Filter

 

Over the years of pour over, we’ve seen plenty of exciting advancements. New drippers, water minerals, and accessories that have changed the way we brew. But when it comes to filters, not a whole lot has changed.

Sure, there are some great brands out there — ones we still reach for every day — but for the most part, they’re all pretty similar. The fundamentals haven’t changed all that much.

That’s why we’re excited to introduce Perme — our own branded filter paper and its unlike anything out there. It doesn’t just tweak the old formula, it rewrites it entirely. From the way it flows, to its materials, to how it interacts — it’s something completely new, and we’re thrilled to finally share it with the coffee world.

 

What is the Perme Filter?

Short for permeable, the Perme Filter is a new kind of filter paper designed specifically for specialty coffee. Made from a blend of polypropylene (PP) and polyethylene (PE), its unique non-woven structure gives it a property that feels almost like a magic trick.

At first, it’s hydrophobic — meaning it repels water. You can pour hot or cold water on it, and it won't pass through. But once coffee is added, it starts to break the surface tension, activating the filter and gradually allowing the water to flow.

This unique behaviour brings a whole new dynamic to coffee filtration, opening the door to brewing techniques we’ve never had access to before — like inverse blooming. But before diving into that, let’s start with how this filter actually works.

 

Oil activated - Polar and Non-polar

The way Perme works all comes down to how water and the filter material interact. Water has a polar structure, while the filter is made from non-polar materials. Polar and non-polar don't mix, that’s why plain water just sits on top of the filter instead of passing through.

Once coffee is added, though, it’s a different story. Coffee is full of natural oils and lipids that are also non-polar. These coat the filter and help break the barrier, letting the water move through gradually. In simple terms: the coffee itself activates the filter and makes the brewing possible.

There are two primary ways you can use Perme, you can brew the traditional way where you add the coffee first, or you can explore a more modern approach with the inverse bloom — where the water is added first. 

 

The Traditional method

The traditional method with Perme is much the same as any pour over: place the filter in your dripper, add your ground coffee, and start brewing. Of course, there’s no need to pre-rinse the Perme.

For the most part, Perme behaves much like paper, but with one important twist: flow is initially restricted. That’s because it takes a little time for the coffee’s oils to activate the filter and make it permeable. How long this takes depends on the coffee — sometimes as quick as 5–10 seconds, other times closer to 30 seconds — more on this later. Once activated, the flow gradually opens up and can actually run quite fast toward the end of the brew. We’ll dive deeper into how different coffees (such as washed and naturals) interact with Perme a little later on.

So what does that early restriction mean for brewing? In our view, it’s a positive. During the bloom — arguably the most critical phase — the restricted flow forces the water to fully interact with the coffee, saturating it completely. This ensures a more even start to extraction and helps capture everything in the grounds. From there, flow opens up and gradually speeds up towards the end of the extraction. Overall, the brew is more consistent, repeatable, and predictable.

We'd recommend giving the bloom at least 45 seconds with the Perme filter, this will allow all the water to pass through the coffee bed before your next pour. 

The Modern Approach (Inverse Bloom)

This is where things get really interesting. If you’ve ever brewed with a Hario Switch or a Clever Dripper, you might have tried an Inverse Bloom — where you add the water before the coffee. With Perme, you can do this too.

We don’t suggest adding all your brew water at once. Instead, just use your bloom portion. For example, in a 15:225 brew ratio, start with about 45 g of water — just enough to saturate the dose properly.

Once you add your ground coffee into the water, give it a quick stir or agitate with a WDT tool or teaspoon. Within a few seconds, and depending on the coffee, flow will begin.

This approach lets you experience pour over in a completely new light, opening up flavours and textures you wouldn’t normally get with traditional papers. In our experience, it’s a fantastic method for highlighting acidity and clarity, but we're excited to see how to you explore this method.

 

What to expect in the cup

First and foremost, Perme’s material (PP and PE) is completely neutral. Unlike traditional paper filters which are made from polar fibres and often leech flavours, Perme is non-polar. The polymers are solid and insoluble, meaning they physically cannot impart flavour. Your coffee takes centre stage — nothing else.

Next, let’s quickly touch on flow again. With Perme, flow is initially restricted with little to no bypass occurring, allowing for maximum extraction in this crucial first phase. Then as the brew progresses, permeability increases and the flow opens up — often finishing faster than most paper filters on the market. And thanks to its non-woven structure, clogging simply doesn’t occur.

So how does this translate in the cup? This is where Perme shines. It delivers an expressive brew with remarkable clarity, letting flavours come through clean and vibrant. It filters incredibly well, so fines are held back, the cup is crisp and transparent — yet still carries a beautiful texture and mouthfeel.

 

Natural vs Washed 

It’s also worth noting that different coffees will interact with Perme in different ways. For example, natural-processed coffees tend to contain more oils than washed coffees, simply because the beans dry inside the whole cherry and absorb more lipids from the fruit.

Those extra oils mean naturals often activate Perme’s permeability faster — sometimes within just a few seconds. Washed coffees, on the other hand, usually carry fewer oils, so they can take a little longer to break the surface tension and get the flow going.

This variation isn’t a flaw — it’s part of what makes Perme so interesting. Washed coffees still work beautifully — they just might take a few seconds longer to get things flowing. Each coffee brings its own character to the way Perme brews and we think this is really exciting.

 

Roast Degree

Similarly, roast degree also affects how Perme behaves. It’s not that darker roasts contain more oils — rather, the roasting process pushes those oils to the surface more quickly than in lighter roasts. This means darker roasts will usually activate the filter’s permeability faster, allowing flow to begin sooner.

Lighter roasts, on the other hand, tend to keep more of their oils locked inside the bean. Because less oil reaches the surface, they can take longer to break the filter’s surface tension, which is why activation and flow may be a little slower.

This difference is completely natural, and just like with processing, it adds another layer of character to how each coffee interacts with Perme.

 

Aged Coffee

One of the most interesting things we’ve discovered — not just about the Perme Filter, but about coffee itself — is what happens as it ages.

During testing, we noticed that coffees two months or more post-roast drained noticeably slower on Perme. Since oils are what activate permeability, we first thought the beans were somehow losing their oils. But oils don’t just vanish — while volatile aromatics escape into the air, lipids themselves don’t simply evaporate. So what was really happening?

After digging deeper, we learned something fascinating: the oils in coffee don’t disappear, they transform. Over time, these lipids oxidise and polymerise — meaning their molecular structure shifts. Fresh coffee oils are fluid and mobile, able to coat the filter and break surface tension with ease. But as they age, they harden and take on a more waxy consistency. In this state, they’re far less effective at activating permeability.

For us, this has been a fascinating reminder that there's still so much to learn about coffee. It might just be our favourite incidental discovery to date.

 

Grinding Finer = Faster Flow? 

It sounds backwards, but with Perme that can sometimes be the case. We’ve seen instances where activation takes longer than expected — especially with coarser grinds. This flips the usual logic of extraction on its head.

Why? It comes back to oils. When you grind finer, more of the oils locked inside the beans are brought to the surface. More surface area means more oils exposed, which helps activate permeability faster. With a very coarse grind, many of those oils remain trapped inside the particles, so it can take longer for the filter to open up.

The result is that, in some cases, grinding finer actually leads to faster flow. And because Perme doesn’t clog, you’ll find you can push grind size finer than you might normally expect — opening up new territory for experimentation and flavour.

 

It's plastic, is it bad for me?

That’s a great question, and a perfectly valid concern. We want to be completely transparent and answer it clearly.

Let's start with the materials. The Perme Filter is made from polypropylene (PP) and polyethylene (PE) — both widely used food-grade polymers. These are the same stable, inert materials found in baby bottles, medical syringes, and food containers. They’re completely insoluble in hot water, flavour-neutral, and safe for direct food contact.

Importantly, the melting points of PP and PE are far above brewing temperatures, which means they remain completely stable during use and don’t degrade or release anything into your coffee.

To create the filter, PP and PE are drawn into ultra-fine fibres, much thinner than a human hair. Instead of being woven like fabric, the fibres are laid in a random web and gently bonded with heat and pressure. The result is a strong, non-woven sheet with consistent structure and porosity — the key to Perme’s unique brewing behaviour.

For added assurance, the Perme Filter has been independently tested by SGS against GB 4806.7-2023 food contact standards (covering overall migration, heavy metals, and sensory tests) and passed all requirements.

 

Binning responsibly 

The Perme Filter is designed for single use, just like traditional filter papers. It's made from recyclable soft plastics, however, because the filter comes into contact with organic material (spent ground coffee), it usually won’t make it through household recycling systems. In most cases, it will need to go in general waste.

That said, PP and PE are among the most stable and widely recycled polymers in the world. If you have access to a specialised recycling stream that accepts used soft plastics, Perme can be collected and processed just like other recyclable plastics.

We always recommend being mindful with disposal:
– Shake out or compost the spent coffee grounds separately.
– Place the used filter into general waste (unless you have access to a local scheme that accepts used soft plastics).

 

A New Chapter In Brewing

Perme has already challenged so many of the assumptions we’ve held about pour over — from how flow behaves, to what oils do as coffee ages, to the way grind size flips our expectations. But this is only the beginning.

What excites us most is not just what Perme can do, but what you will do with it. Every coffee, every brew method, and every curious adjustment will reveal something new. We’ve built this filter to open doors, not close them — to give brewers a tool that behaves differently, so you can explore differently.

So now it’s over to you. We can’t wait to see how the specialty community uses Perme, the discoveries you make, and the flavours you unlock.

Purchase your Perme Filter Here.