Dust-mite encasements: how pore size works

The short version

A mite-proof cover is a fabric barrier. What makes it one, according to the lab literature we found, is how small the gaps between its fibres are. One study gives a figure, and none of the product pages we read repeat it. This page sets out what that study says, what the allergy bodies say covers are for, and what makers do and do not state. We work from documents and have not tested any products.

What the one pore-size study found

A 1999 paper in the Journal of Allergy and Clinical Immunology (PMID 9949312, abstract retrieved 2026-11-14) set out to develop a way of testing breathable encasement fabrics. Dust samples with a known quantity of allergen (Der f 1, Der p 1 and Fel d 1) were pulled across a variety of fabrics using a modified dust trap, with airflow controlled by a vacuum pump. A filter downstream collected whatever passed through, and it was measured by ELISA. The fabrics “were obtained from manufacturers and specialty catalogs”.

The abstract reports two results. “Dust mite allergens (Der f 1 and Der p 1) were blocked below detectable limits by fabrics of less than 10 microm in pore size.” And “Fabrics with an average pore size of 6 microm or less blocked cat allergen (Fel d 1).” It also notes that as average pore size decreases, airflow through a fabric becomes restricted, and concludes that tightly woven and nonwoven synthetic fabrics “can block common indoor allergens but still allow airflow.”

That is the only pore-size figure in our sources, and it is one study’s lab result, not a regulation or a standard. The abstract does not say how fabrics behave after washing, at seams or at zips.

A second fabric study

A 2004 study in Allergy (PMID 15291905) tested eleven commercially available fabrics made for allergen avoidance against regular cotton, using the same kind of dust-trap method for Der p 1 and Fel d 1. It reports that all the tightly woven and laminated materials “were able to control mite allergen permeability allowing air passage” but differed in how much cat allergen got through. Laminated fabrics controlled both allergens but “did not allow air permeability.” Its conclusion is that the actual properties of encasement products need to be known to balance allergen avoidance, disease control and sleep comfort. The abstract gives no pore sizes.

Together the two abstracts describe a trade-off: a fabric can block allergen by being tightly woven or by being laminated, and the laminated route costs breathability.

What the allergy bodies say

AAFA’s dust mite allergy page (retrieved 2026-11-14) recommends covering mattresses and pillows with “zippered allergen-barrier covers”, made of material with “pores too small to let dust mites and their waste product through.” It gives no number. It also says that even if you cover your mattress and pillows, dust mites can still live in your bedding, and advises washing sheets and blankets weekly in water at least 130 degrees F, and keeping indoor humidity between 30 and 50 percent.

The NIEHS page (retrieved 2026-11-14) says dust mites cannot be completely eliminated “no matter how clean a home is”, but numbers can be reduced, including by encasing the mattress and pillows in “dust-proof or allergen impermeable covers”, keeping humidity at or below 50 percent, and washing bedding weekly in 130 to 140 degree F water.

What a certification adds

The Asthma & Allergy Friendly program’s science page (retrieved 2026-11-14) lists separate bedding standards, including a pillow encasing (ASP:02-02), a mattress encasing (ASP:02-05) and a mattress cover, partial pad (ASP:02-12). The principles it lists include an effective barrier to allergen passage, breathability, and washability. For a mattress cover it names water vapour transmission and dust mite allergen accumulation rate. It also says sheets and duvet covers are not sufficient allergen barriers alone. The page gives no numeric limits or test methods for bedding, so we cannot tell you what pore size the program requires. For how the mark works, see the Asthma & Allergy Friendly guide and how to read allergy-certified bedding labels.

What makers state about pore size

We checked every mattress protector record on this site for a stated pore size, micron figure or allergen-blocking test. Each is a maker statement, read from the maker’s page:

• Purple Waterproof Mattress Protector (maker page, 13 November 2026): the maker calls its fabric hypoallergenic and anti-microbial. The record states no pore size. The record notes the page also makes dust-mite protection wording, which we do not quote.
• Coop Home Goods Ultra-Tech (maker page, browser-captured 13 November 2026): states OEKO-TEX STANDARD 100 for every component; no pore size, and no hypoallergenic wording on the product page.
• Avocado Organic Waterproof Mattress Protector (maker page, 13 November 2026): states organic cotton around a polyurethane membrane and GOTS and OEKO-TEX certificates; no pore size or hypoallergenic wording on the page.
• TEMPUR-Protect (maker page, 13 November 2026): polyester fabric with a waterproof polyurethane laminate; no pore size and no certification found.
• Parachute Cotton Mattress Protector (maker page, browser-captured 14 November 2026): 100% cotton, OEKO-TEX STANDARD 100 stated; not waterproof; no pore size.

A separate record for Naturepedic’s waterproof protector quotes its page as “helps guard against spills, dust mites, and everyday allergens” and notes that no pore size is stated. For what these records show about the protectors themselves, see our mattress protector page. The word “hypoallergenic” has no legal definition; see what hypoallergenic means.

Not stating a pore size does not mean a cover fails to block mite allergen. It means the page does not let you check. Certification marks such as OEKO-TEX address harmful substances in textiles, not allergen blocking; see what OEKO-TEX STANDARD 100 means.

What covers have shown in trials

These are abstracts only, reported as the authors state them.

• An adult trial (PMID 14656350, 2003) randomised mite-sensitised asthmatics to allergen-impermeable or placebo covers for 12 months. Der p 1 concentrations at the end were not significantly different between groups, and there was no effect on peak flow or asthma symptoms. The authors say that allergen-impermeable bedding alone cannot be recommended as an effective way of relieving asthma symptoms in this group.
• A trial in young children (PMID 12153962, 2002) of 1,282 allergic pregnant women found less night cough in the second year of life with active covers (adjusted odds ratio 0.65; 95% CI 0.4 to 1.0), with no effect on other respiratory symptoms, atopic dermatitis or sensitisation.
• The 8-year follow-up (PMID 22023655, 2012) reports lower Der f 1 but not Der p 1 in the active group, a temporary decreased risk of asthma symptoms at age 2, and no reduction in hay fever, eczema or allergic sensitisation.
• A 2025 systematic review (PMID 40774466) of home interventions for childhood asthma found high heterogeneity and only three high-quality studies. It says a significant effect was found in two high-quality studies on mattress covers, and calls mite-impermeable covers promising.

Whether a cover helps a particular person is a question for a doctor or allergist.

How to use this when you shop

Read the maker’s product page for a stated pore size, a named test, or an allergen-barrier certification, and treat “mite-proof” without any of these as an unsupported maker claim. Remember that the covers in the studies were encasements, and that a cover does not replace washing and humidity control. For the wider picture see why dust mites are the usual bedding allergen, pillow protectors, hypoallergenic bedding, hypoallergenic mattresses, pillows, the laundry routine, thread count and allergies, the hypoallergenic bedroom and nursery bedding.

What we did not find

We found no standards-body pore-size threshold, no pore sizes for the products on this site, and no independent test results for them. The limits of the studies are listed under unknowns.