What Does Pore Size Mean in Allergy Proof Bedding?

If you've been diagnosed with dust mite allergies, your doctor has probably told you to encase your mattress and pillows in allergy-proof covers. Great advice. But then you go online and encounter terms like "pore size," "microfiber," "micro-weave," and "laminated" — and suddenly a simple purchase feels like a science exam.

We field calls about this every day. Let's clear it up once and for all.

Why Allergy Bedding Works

Dust mites, their feces, pet dander, mold spores, and pollen all collect in fiber surfaces — your mattress, pillows, and duvet are effectively allergen reservoirs. You can't see, feel, or smell these particles, but every time you move in bed, you puff them into the air and breathe them in all night.

Allergy-proof covers create a physical barrier between you and those allergens. The less of them you breathe in, the less they can trigger your symptoms. Paired with weekly washing of your sheets and pillowcases, a good set of encasements reduces your allergen exposure, and the barrier starts working from the very first night.

Two Ways to Make a Fabric Allergy-Proof

There are two fundamentally different approaches to building an allergen barrier into a fabric — and understanding the difference makes choosing the right cover much easier.

1. Micro-Weave Fabrics

A micro-weave fabric is woven so tightly that the spaces between the fibers — the pore size — are too small for allergen particles to pass through. The fabric itself is the barrier. No coating, no membrane. Just an exceptionally tight weave.

Pore size is measured in microns (one micron = one millionth of a meter). For context, a human hair is about 70 microns wide. Dust mite fecal particles, the main source of dust mite allergen, are roughly 10 to 40 microns across. Standard cotton sheets have pore sizes in the hundreds of microns, which is why dust mite allergens pass right through them.

According to the AAAAI and ACAAI practice parameter on dust mites, a woven fabric needs a mean pore size under 10 microns to effectively block the major dust mite allergen. Both of our AllergyCare™ micro-weave fabrics are well below this threshold.

2. Laminated / Membrane Fabrics

A laminated fabric bonds a urethane membrane to the back of the base fabric using heat. It's the membrane — not the fabric — that provides the allergen barrier. Because the membrane is a complete, impenetrable layer, laminated covers don't have a pore size. They block everything, including liquids, making them fully waterproof as well.

The trade-off is feel and breathability. Laminated covers tend to run warmer than micro-weave covers because the membrane reduces airflow. For most adults, micro-weave is more comfortable for everyday sleep. For children's beds or situations where waterproof protection is needed, laminated covers are the right choice.

Pore Size and Fiber Type: Why Cotton and Polyester Are Different

Not all micro-weave fabrics are the same — and fiber type is the main reason why.

Polyester is a very strong synthetic fiber. Because it's so strong, it can be woven much more tightly than natural fibers without breaking. This means polyester micro-weave fabrics can achieve smaller pore sizes.

Cotton fibers are naturally softer and more flexible, but they're not as strong under tension. You can't weave cotton as tightly as polyester, so all-cotton allergy covers will always have a slightly larger pore size than equivalent polyester fabrics. That said, our cotton fabrics are still well within the effective range for dust mite protection.

Organic cotton adds another consideration: it's grown without synthetic pesticides or fertilizers and processed without dyes or chemical treatments. This makes it the right choice for people with chemical sensitivities — even though its pore size is slightly larger than conventional cotton.

Our AllergyCare™ Fabric Lineup: Pore Sizes Compared

Here's exactly how our current fabrics compare — including pore sizes, construction type, and what each is best suited for.

All three fabrics provide effective protection against dust mite allergens. The differences come down to comfort, feel, and whether you need waterproof protection — not whether one works and another doesn't.

Does a Smaller Pore Size Mean Better Protection?

This is the question we get most often — and the answer is: not necessarily, once you're below the threshold.

For dust mite allergen, a mean pore size under 10 microns is effective. Going from 5.3 microns to 4.6 microns doesn't meaningfully improve your protection against dust mites.

Where pore size does make a difference is for smaller allergens. Cat allergen travels on much smaller particles than dust mite allergen, and the same practice parameter notes that blocking it requires a mean pore size under 6 microns. Both of our cotton micro-weave fabrics meet that tighter mark as well, so they're a good fit if you also react to cats.

Care Tips for Allergy Bedding

• Micro-weave covers (cotton and organic cotton): open the zipper and turn the cover inside out, then wash on a gentle cycle to protect the tight weave. Avoid chlorine bleach, which can break down fibers and widen pore sizes over time. Tumble dry on low or medium heat, never high.
• Laminated covers (Stretch Knit): leave the cover right-side out. Tumble dry on low heat, never high — the urethane membrane is heat-bonded to the fabric, and high temperatures can separate the bond. No chlorine bleach.
• All covers: skip fabric softener and dryer sheets, and make sure the cover is completely dry before it goes back on the bed.
• How often: pillow covers every 4 to 6 weeks; mattress and box spring covers once or twice a year, or after a spill. Wash sheets and pillowcases weekly in warm water (no hotter than 120°F) with De-Mite Laundry Additive, or use Allersearch Allergen Wash in place of your regular detergent. You don't need scalding-hot water to remove dust mite allergen.

For step-by-step instructions, see How to Care For Your New Dust Mite Covers.

The Bottom Line

Pore size tells you how tightly a micro-weave fabric is woven and how small a particle it can block. For dust mite allergy protection, you need a mean pore size under 10 microns — both of our AllergyCare™ micro-weave fabrics meet this standard comfortably. Laminated covers like Stretch Knit skip the pore size question entirely by using a complete membrane barrier.

The right fabric for you comes down to how you sleep, whether you need waterproof protection, and whether you have chemical sensitivities. If you're not sure, we've been helping people make this decision since 1989.

Want the complete picture? Everything on this page is part of our free Practical Guide to Allergy-Free Living, built on allergy expertise we've been sharing since 1989 and covering dust mites, pet dander, air quality, laundry, and more. Start at the beginning or jump to the section that matters most to you.

Call us at (800) 771-2246 — we're happy to walk you through it.

Shop all AllergyCare™ mattress covers →

→ Not sure which cover is right for you? Read our complete buying guide.

Sources
AAAAI and ACAAI — Environmental Assessment and Exposure Control of Dust Mites: A Practice Parameter: https://pmc.ncbi.nlm.nih.gov/articles/PMC5156485/
AllergyCare Cotton pore size analysis (PMI): AllergyCare_Cotton_Pore_Size_Analysis_8.26.2025.pdf

Medical Disclaimer: The information on this page is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider — such as an allergist or your primary care physician — before making changes to your allergy management plan, starting new treatments, or if you have questions about a medical condition. In the event of a severe allergic reaction or anaphylaxis, call 911 or your local emergency number immediately and use an epinephrine auto-injector if one has been prescribed.