What is the pore size range of TFF Membrane Cassettes?

If you’ve ever worked in biotech, pharma, food and beverage processing, or even water treatment, you’ve probably encountered TFF (Tangential Flow Filtration) membrane cassettes. If you’re new to this space, one of the first questions you’ll ask is: what’s the pore size range of these things? As someone who’s been supplying TFF cassettes for years, I get this question all the time—and it’s not a one-size-fits-all answer. Let’s break it down, no stuffy jargon, just real talk from a supplier who’s seen what works (and what doesn’t) in the field.

First, let’s keep this simple. TFF works by pumping liquid parallel to the membrane surface, so only small particles pass through (the permeate) while bigger stuff stays behind (the retentate). The pore size is what determines which gets separated. Now, the range isn’t static—it spans from microfiltration (MF) all the way to ultrafiltration (UF), and even a little into nanofiltration (NF) territory for some specialized models. But let’s get specific, because that’s where confusion happens.

Starting with the big end: microfiltration TFF cassettes. Most of our clients first reach for MF when they need to separate things like cells, bacteria, or large cell debris from a solution. The pore size here generally lands between 0.1 micrometers (um) and 10 um. Wait, that’s a wide range, right? Let’s narrow it down to the common ones we ship daily. If you’re filtering mammalian cells (like in monoclonal antibody production), 0.1 um to 0.22 um is the sweet spot. Why? Bacteria are around 0.5 um in size, so 0.22 um is the standard for sterilizing filtration—hence our popular 0.22um Microfiltration Cassettes, designed exactly for that. If you’re dealing with smaller bacteria or even larger cell aggregates, stepping up to 0.45 um makes sense, which is another option in our MF line.

Now, what if you need to go smaller? That’s where ultrafiltration comes in. UF TFF cassettes have pores that are measured in molecular weight cut-off (MWCO) instead of physical um, which is a different way to think about it. MWCO is the size of the smallest molecule the membrane will retain, usually expressed in kilodaltons (kDa). Our UF range starts at 1 kDa (great for concentrating small proteins) and goes up to 1000 kDa, which works for larger proteins like antibodies. But here’s the thing: a lot of people mix up MF and UF, so it’s important to note that MF pores are big enough to see with a good microscope, while UF pores are so tiny they can’t be measured as individual holes, just by what they hold back.

Before we dive deeper, let’s talk about why pore size matters so much. Pick the wrong one, and you’ll either lose your product to permeate (if pores are too big) or slow down your filtration to a crawl (if pores are too small, leading to more fouling). I’ve seen a startup in biotech waste weeks of work because they used a 0.1 um cassette when they needed 0.45 um—they thought smaller was better, but the tiny pores kept clogging with cell debris. That’s why matching pore size to your application is non-negotiable.

Now, let’s get into the specifics of our cassettes, since that’s what I know best. Our MF line, which includes everything from flat sheet cassettes to single-use options, has pore sizes that cover that 0.1 um to 10 um range. The 0.1um Microfiltration Cassettes are perfect for clarifying cell culture supernatants without losing the target protein, because they catch cells and debris while letting the protein pass through. If you’re doing a final sterilization step, the 0.22 um ones are your go-to—they’re tested to remove 99.999% of bacteria, so you don’t have to worry about contamination. For industrial applications like beer clarification or removing yeast, our Flat Microfiltration Cassettes (which can handle higher flow rates than single-use ones) come in 1.0 um and 5.0 um, ideal for that.

Wait, I should also mention that pore size isn’t the only factor—membrane material plays a role too. We use things like polyethersulfone (PES) for most MF and UF cassettes, because it’s durable, has consistent pore sizes, and resists fouling. But for certain chemicals, we offer PVDF or mixed cellulose ester (MCE) options, which have slightly different pore size profiles. For example, our Microfiltration Membrane line includes MCE membranes that are often used for water testing, with pore sizes like 0.45 um and 0.8 um, perfect for catching microbes in drinking water.

Another point: when people ask about TFF cassette pore size, they often forget about the “nominal” vs “absolute” pore size. Nominal is the average size, while absolute is the maximum size of a particle that will be retained. All of our cassettes are tested to have consistent absolute pore sizes, so you don’t get surprises when you scale up. That’s a big deal—laboratory-scale filters might have slightly variable pores, but our production-grade cassettes are made with tight quality control, so every cassette in a batch has the same pore size range.

Let’s cover some common applications to put this all in context. If you’re processing a biologic: starting with UF to concentrate your antibody (100 kDa MWCO), then polishing with a UF cassette, and maybe a final sterilization step with a 0.22 um MF cassette. If you’re in food and beverage: clarifying fruit juice with a 1.0 um flat sheet cassette to remove pulp, or filtering beer with a 0.5 um cassette to get that clear, crisp taste. If you’re in environmental testing: using our 0.45 um Microfiltration Cassettes to catch coliform bacteria in water samples. All of these fall right into the range we’ve been talking about.

Now, let’s address a question I get all the time: can I get a TFF cassette with a pore size outside of this range? For MF, the upper limit is around 10 um—anything bigger than that is usually a different type of filter, like a depth filter, not a TFF cassette. For UF, the lower MWCO is about 1 kDa, and the upper is 1000 kDa; below 1 kDa is nanofiltration, which is used for desalting or removing small organic molecules, and we do offer NF cassettes too, but that’s a separate category.

I should also touch on fouling, because it’s tied to pore size. When pores get clogged, the effective pore size shrinks, which makes filtration slower. To fight that, we design our cassettes with open-channel flow paths, so liquid moves across the membrane instead of straight through, reducing the chance of debris getting stuck in the pores. That’s why even if you pick the right pore size, the cassette’s design matters. For example, our Microfiltration Flat Sheet cassettes have wider channels than single-use ones, so they handle more viscous solutions (like concentrated cell lysate) without fouling as much.

At the end of the day, the pore size range of TFF membrane cassettes is roughly 0.1 um (MF) all the way down to less than 0.001 um (UF, when converted from MWCO), with specialized options in NF. But the key is matching that range to your specific application—don’t just pick the smallest or biggest available. If you’re not sure which pore size you need, that’s what we’re here for. We’ve worked with hundreds of clients, from small startups to large pharma companies, to pick the right cassette for their process. Whether you need a 0.1um Microfiltration Cassette for cell clarification, a Flat Microfiltration Cassette for industrial scale, or a custom UF cassette for protein concentration, we’ve got you covered.

If you’re ready to stop guessing and get a cassette that works for your process, reach out to our team to chat through your needs. We don’t do one-size-fits-all solutions, and we’re happy to walk you through pore size options, membrane materials, and flow rates to make sure your TFF setup is as efficient as possible. No pressure, just real advice from a supplier who’s been in this game long enough to know what works.

References

1. Tangential Flow Filtration: Principles and Practice, 2nd Edition, M. Cheryan, 1998
2. Microfiltration Membrane Technology and Applications, J. Li, 2010
3. Pall Corporation TFF Cassette Product Guide, 2022
4. "Pore Size and MWCO: Key Differences in Membrane Filtration", BioProcess International, 2021