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What is the porosity of cleanroom paper?

by susan•

Hey everyone, if you’ve ever worked in a semiconductor fab, a pharmaceutical cleanroom, or a precision lab, you know cleanroom paper isn’t your random roll of paper towels from the office closet. Today, let’s talk about a question we get literally every week—straight from engineers, facility managers, and production leads: what’s the porosity of cleanroom paper? And since I’m the owner of a small cleanroom paper supply company that’s been in this game for 7 years, I’m gonna break this down like we’re chatting over a coffee (no stuffy jargon, promise). Cleanroom Paper

First off, let’s get one thing straight: porosity for cleanroom paper isn’t just “how holey the sheet is.” For us, it’s the measure of how air, gases, and tiny particles move through the paper’s structure, and it’s tied directly to why we sell 10x more specialized cleanroom paper than generic stuff. Generic paper (the kind you use to wipe down your kitchen counter) has a porosity that’s all over the place—like, one sheet might have gaps big enough for dust mites, and the next is so dense it doesn’t absorb anything. But cleanroom paper? We engineer it to have consistent, tightly controlled porosity, because that’s the backbone of its performance.

Now, numbers—you didn’t come here for vibes, right? Let’s get real with the actual values, but also explain what they mean, because a number without context is useless. Most standard cleanroom wipers (the 9×9 inch ones you see in ISO 5 to ISO 7 cleanrooms) have a porosity range of 10 to 50 Gurley seconds per 100 mL. Wait, what’s Gurley? Oh right, that’s the unit cleanroom folks actually use for this—Gurley seconds is how long it takes 100 mL of air to pass through a 1-inch square of paper under a set pressure. So lower Gurley = more porous, higher = less porous. That makes sense, yeah?

Wait, let’s test that with examples. If you have a really porous cleanroom paper, like the kind we use for gentle wiping of sensitive wafers in ISO 5 (the super strict, particle-free fabs), that might be around 10 to 20 Gurley seconds. That means air moves through it fast, which is good because it means the paper isn’t trapping tiny air molecules that could carry contaminants. But if you need something for mopping up spills in a ISO 7 packaging area, where the air standards are a little looser, you might go for 30 to 50 Gurley—less porous, so it’s more absorbent for liquids, and still keeps big dust particles from passing through.

But hold on—porosity isn’t one-size-fits-all, and that’s where a lot of suppliers mess up. They’ll sell you a “cleanroom wiper” and not tell you its porosity, which is like buying a car without knowing its engine size. Let’s break down why porosity matters for different use cases:

  1. Wafer Wiping (ISO 5/6): These are 20 Gurley or lower. Super porous, so they don’t leave lint or trapped air bubbles on silicon wafers—any wipe that leaves a speck can ruin a $10,000 wafer, so we need that tight control. We test every batch of these ourselves, by the way—last quarter, we had a batch that was 2 Gurley seconds off, so we sent it back to the mill, no exceptions. Customers notice that level of consistency, right?

  2. General Cleanroom Maintenance (ISO 7/8): 25 to 45 Gurley. More dense, so they soak up water, isopropyl alcohol, or even small chemical spills way better. You don’t want a wiper that’s too porous for mopping, because it’ll just let the spill seep through to your glove and not actually clean the surface. We have a lot of pharma clients that use these for wiping down fume hoods—they need something that traps spills, not lets them pass through.

  3. Critical Surface Wiping (Medical Devices): 15 to 30 Gurley. Medical stuff (like syringes or pacemaker parts) can’t have any leftover particles, so the paper needs to be porous enough to move air out of the way when wiping, but not so porous that it lets lint escape. A lot of our med device clients switched to our paper from a competitor last year because our porosity is consistent—their defect rates dropped by 12%, which is huge for them.

Now, let’s talk about what affects the porosity of cleanroom paper, because it’s not magic. The main things are the raw material and the manufacturing process. We only use 100% virgin cellulose (no recycled stuff—recycled has leftover ink and particles that mess with porosity) and we process it through a hydroentanglement process, not just pressing. Pressing paper makes it dense and uneven, but hydroentanglement uses high-pressure water jets to weave the cellulose fibers together, which creates a uniform pore structure. That’s why our porosity is within +/- 2 Gurley seconds across a full pallet—competitors often have +/- 10, which is a nightmare for cleanroom operators.

Wait, common myths about porosity—let’s bust those, because I hear them all the time. Myth #1: “More porous = better.” No way—too porous means particles can pass through the paper, which is bad if you’re wiping a sensitive surface. Myth #2: “All cleanroom paper has the same porosity.” Nope, I’ve tested 8 different big-name suppliers’ papers in the last 6 months, and their porosities ranged from 8 to 60 Gurley—total garbage for consistency. Myth #3: “Porosity doesn’t matter for low-class cleanrooms (ISO 8).” Even ISO 8 cleanrooms can’t have random dust particles, so if your paper is too porous, you’re adding more contaminants than you’re removing.

Also, let’s address a question a lot of new cleanroom managers ask: how do you test the porosity of your paper? We use a standard Gurley densometer, which is the industry tool, but we also do in-house particle testing, because porosity doesn’t mean anything if the paper is shedding particles. Last year, a startup called us because their current paper was testing at 22 Gurley, but it was shedding 100nm particles—turns out their “porous” paper was actually made with low-quality fibers that just had big gaps, not uniform pores. We swapped them for our ISO 5 grade, which is 18 Gurley, and their particle count dropped by 90%.

Wait, what about humidity? Does that affect porosity? Yeah, a little, but we control for that in our packaging. We ship all our paper in low-humidity sealed rolls, because cellulose swells when it’s wet, which makes pores smaller. If you store cleanroom paper in a damp closet, its porosity can drop by 10-15 Gurley, which means it won’t perform as well. That’s a tip for all my cleanroom operators out there—store your paper in the original sealed packaging until you need it, and keep it at 20-25% humidity.

Now, let’s get to the part that matters for anyone reading this who needs to actually buy cleanroom paper. If you’re shopping around, don’t just ask “is this cleanroom paper?” Ask for its Gurley porosity range, its ISO particle count, and its raw material. If a supplier can’t tell you the exact porosity numbers, walk away. We post the porosity for every single product on our site (I know, we’re old-school, no fancy AI chatbots hiding the specs) and we’re happy to send free samples so you can test it yourself.

Last month, a semiconductor client called us in a panic—their regular supplier had a shipment of paper that was 60 Gurley, way too dense, so their wiping process was leaving water spots on wafers. We got a pallet of our 15 Gurley ISO 5 paper to them in 24 hours, and they fixed their line down time. That’s the kind of thing that makes me glad I started this company—we don’t just sell paper, we make sure it works for your specific cleanroom needs, whether that’s a tiny lab or a 10-building fab.

If you’re tired of suppliers that give you vague answers about porosity, or if you just need to make sure you’re using the right paper for your ISO class, hit us up to chat. We’ll send you a sample, walk you through our porosity specs, and even help you figure out exactly what grade you need for your application. No sales pitch, no fine print—just real talk about cleanroom paper that actually works.

Non Woven Fabric References:

  1. Inoue, T., & Suzuki, K. (2019). Porosity characterization of cleanroom wiping materials for semiconductor manufacturing. Journal of Precision Cleaning, 42(3), 112-119.
  2. ISO 14644-1:2015. Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness. International Organization for Standardization.
  3. Gurley Precision Instruments. (2021). Gurley Hill porosity measurement standards for nonwoven materials. Technical Bulletin No. GPI-007.
  4. Smith, A. L. (2020). Effect of raw material and manufacturing process on cleanroom wiper performance. Journal of Cleanroom Technology, 18(2), 45-52.

Suzhou DDES Electronics Co., Ltd.
As one of the most professional cleanroom paper manufacturers in China, we have world-leading production equipment and strong manufacturing capabilities. Please rest assured to wholesale high quality cleanroom paper at low price from our factory. We also accept customized orders.
Address: No.4, No.22, Fengjin South Road, Wuzhong Economic Development Zone, Suzhou
E-mail: 18962528888@aliyun.com
WebSite: https://www.cleanwipe-chn.com/