ALLERGEN-BARRIER PILLOW AND MATTRESS ENCASINGS
There is much confusion about the different types of allergen-proof pillow and mattress encasings on the market today. Allergen-barrier encasings vary widely both in the type and quality of their fabric, and in the quality of their sewing construction.
FABRIC
There are four basic types of materials used to manufacture allergen-barrier encasings: vinyl, laminates, woven microfiber fabric, and non-woven microfiber fabric. Within each material type, there are differences in fabric quality and sewing construction that determine their effectiveness.
Vinyl encasings are inexpensive and effectively block allergen escape. However, because they are stiff and noisy, and do not allow air or water vapor passage, they are uncomfortable to sleep on. As a result, most individuals remove them from a pillow or mattress after a day or two. They are suitable, however, for encasing a box spring, where one is not sleeping directly on the plastic. The vinyl should be of sufficient thickness as to not tear easily.
Vinyl can be made more comfortable for use on a mattress by covering it with a mattress pad, and this is a reasonable option for patients with limited finances, if they faithfully wash the pad in hot or warm water weekly to prevent mite growth and allergen accumulation in the pad itself.
Laminate encasings are used less often than previously (since the advent of microfiber encasings) but are still sold. They are made by laminating (fusing) a plastic-type membrane—usually polyurethane—to a fabric. The membrane side is against the pillow or mattress, and the fabric side is exposed, beneath the bed linens. Although slightly more comfortable than vinyl, they are somewhat stiff, have only very minimal water vapor permeability, and are not air or heat permeable, so that many patients with skin allergies feel worse with such encasings. Also, once an encasing of this type is zipped closed around a pillow, air becomes trapped within the encasing. Pressing on the pillow may then force air (and allergen) out through the zipper webbing.
An additional problem with laminate encasings is that they occasionally de-laminate; with repeated washing and drying the urethane membrane can separate from the fabric onto which it had been coated, making the encasing unusable. Another issue is the type of fabric onto which the membrane is laminated. A laminated terry cloth encasing is deep enough to accumulate allergen and allow mite colonization.
Mission: Allergy encasings do not use laminates.
Woven Microfiber encasings are now the most commonly used allergen-barrier encasings. These fabrics are woven from yarns each of which comprise many (100-200) ultra-thin (micro-denier) filaments. The fibers are so thin and so tightly woven that there is no space between the weave of the yarns large enough to allow the passage of allergen particles. Since the microfiber fabric itself is acting as a filter that prevents allergen escape, encasings made from microfiber fabric do not need the urethane membrane. Without the membrane they are truly breathable; both air and water vapor can pass freely through the fabric. They are therefore imperceptible to the user.
The problem for the consumer is that not all microfibers are the same. Photos taken through a microscope of fabrics illuminated from below reveal that items sold as barrier fabrics vary considerably in the tightness of their weave. This is the result of differences in the number of yarns per inch, the number of filaments per yarn, and the diameter of each of those filaments. In fact, most of the so-called microfiber encasings on the market are not true microfibers, according to textile industry standards defining microfiber fabrics as those woven from yarns made of filaments no more than 1.0 denier each.
Mission: Allergy Premium encasings are true microfiber fabrics, made from 0.3 denier filaments, with over 200 filaments
per yarn.
A study done at the University of Virginia showed that microfiber fabrics with a mean pore size less than 10 microns blocked mite allergen (Der p1), and those with a mean pore size of 6 microns or less also blocked cat allergen (Fel d1). Mean pore size may not be the best indicator of allergen impermeability, however, because it is only an average size, and does not indicate the total number of pores (are there only a few or very many pores?), the distribution of pore sizes around that mean (are all of the pores close to the average in size, or are some of the pores very large?), or the “tortuosity” of the pores (how straight are the channels?) , all of which can influence the likelihood of an allergen particle passing through the fabric. While pore size may be a useful rule of thumb, in the final analysis the issue is simply whether measurable mite and cat allergen can be sucked through a given fabric.
Mission: Allergy encasings prevent the passage of any measurable mite and cat dander allergen.
Non-woven Microfiber encasings are the final type of encasing. In contrast to a woven fabric where the long warp and weft yarns are alternately woven above and below each other on a loom, non-woven fabrics are manufactured by fusing a mass of overlain fiber filaments to each other using heat, chemicals, and pressure. Examples of typical (not microfiber) non-woven fabrics include felt, and the fabrics used in some diapers, surgical gowns, vacuum cleaner bags, carpet backings and air filters. Non-woven fabrics are generally inexpensive, but they lack the strength of woven fabrics.
Non-woven fabrics made from ultra-thin filaments (“non-woven microfiber”) can prevent allergen passage, and are commonly sold as allergen-barrier encasings. They are recognizable by their thickness—having something of the look and feel of a thick paper towel—and by the embossed pattern on their surface, the result of their compression during manufacturing. However, although these non-woven microfiber fabrics are capable of blocking allergen escape from a pillow or mattress, they have a very significant problem: their thickness and structure are such that dust mites can actually enter into and colonize the fabric itself. Non-woven encasings in use by patients for over 1 year often contain very high levels of mite and cat allergen on their surface, levels sufficient to cause allergy symptoms. This is perhaps not surprising given the observation in the laboratory that mite feces placed on a tightly woven microfiber encasing are easily wiped off, whereas mite feces placed an a non-woven microfiber encasing are simply rubbed into the large spaces within the fabric. These findings suggest that non-woven microfibers do not succeed in reducing allergen exposure, and should not be used for allergen avoidance.
All Mission: Allergy encasings are woven (not non-woven) and do not allow mite penetration or allergen accumulation.
SEWING CONSTRUCTION
Sewing construction is a final important variable. Poor sewing construction of some encasings results in gaps of a half-inch or more at the ends of the zipper, providing an opening for the escape of allergen. Higher quality encasings lack such defects. Other desirable features include bound seams to prevent the escape of the allergen through the seam stitching, and an interior zipper flap of barrier fabric that falls into place beneath the zipper, preventing the escape of allergen through the zipper webbing. When encasings lack such zipper flaps, their manufacturers often advise the purchaser to place tape over the zipper. Finally, extra-long zippers make placement of an encasing on a mattress easier than that of an encasing where the zipper only extends one width of the mattress.
All Mission: Allergy encasings have bound seams and zipper flaps. Mission: Allergy mattress encasings have zippers that are 50% of the mattress’ circumference in length.