Types of Allergen Barriers
Allergen Barriers are placed under your sheets and pillow cases and cover mattresses, pillows and boxsprings. They provide a one-of-a-kind barrier between you and the dust mite allergens in your bedding while you use your traditional pillow cases and bed sheets.
- Tightly Woven Fabric - The tightly woven materials have such a small pore size (openings between yarn fibers) that dust mites and their waste can not penetrate through, yet air and moisture easily pass through for comfort. Fabrics can be synthetic such as Polyester, natural fiber such as Cotton or a combination of materials.
- Non-Woven Materials - Materials such as polypropylene are "Melt Blown" to provide a layer fabric system. These materials act like a filter fabric to trap dust mites and their waste and allow air and moisture to pass through. The quality of these materials vary greatly and can be throw away single use products or have short term durability. Washing may cause pilling of the fabric. They are stiffer than Polyester and Cotton fabrics and can make "noise" as you move on the bed.
- Vinyl, Urethane Membrane and Coatings - Vinyl sheeting does not allow air flow through the fabric and would be "hot and Clammy" to sleep on as well as making noise when you move on the bed. You certainly wouldn't want to sleep on a pillow encased in vinyl. Other fabrics with Urethane (plastic) coatings or synthetic membranes attached to the fabric may offer some air permeability, but are not good at allowing moisture to pass through. These materials will cause pillow encasements to balloon around your head and force air and allergens out of zippered areas. These products may be hot to the skin, stiff and uncomfortable because they do not allow moisture released from the surface of our bodies to pass through. The vinyl/urethane coating may produce an odor and release chemicals into the air from off gassing that may be a problem for people with sensitivities to odors or chemicals.
There are many types of tests that can be done on allergen barriers. Testing is important to demonstrate to the consumer that the product claims are legitimate and the product has demonstrated it is effective as an allergen barrier. Some companies perform one test to make their claims, while others do multiple tests. We believe that no single allergen barrier test by itself will indicate the quality and effectiveness of a pillow or mattress encasement due to the variability of fabrics and construction of the finished product. For example a fabric can have a low pore size which is good, but have poor air/moisture permeability making the product uncomfortable. A product's fabric can test well, but seam and zipper construction may be poor and lead to reduced effectiveness and durability. When evaluating an Allergen Barrier, look for products that are tested in multiple ways as an indicator of high performance. Here are the most common tests used to claim effectiveness for Allergen Barrier pillow and Mattress encasements.
- Thread Count - Some retailers and manufacturers of allergen barriers note the thread count of a fabric as a means to indicate or promote their effectiveness as an allergen barrier. This is common for Cotton fabrics. The thread count of a fabric is not an indicator of a fabric's effectiveness at blocking allergens. A thread count is the combined number of yarns woven in the lengthwise (weft) direction and crosswise (filling) direction in a square inch of fabric. So, if 103 yarns are in the weft direction and 162 yarns are in the filling direction, then the fabric has a thread count of 265. The problem with using thread count is that there is great variability in yarns and weaving of the fabric. Yarns vary in diameter (thin or thick), type (textured or smooth, spun or filament), and the fabric can have varying types of weave patterns (plain, twill or sateen) or fabric finishes. For example, if a fabric has a thread count of 250 with thicker diameter yarns, it will be more dense than a fabric that has a thread count of 250 with thinner diameter yarns. Both fabrics have the same thread count of 250, but the fabric with thinner diameter yarns will have more space between the yarns (higher pore size) and will be less effective at blocking allergens through the fabric. Thread count is a description of construction of the fabric and not a measurement of performance of the fabric and can not be used to compare fabrics or make claims as to their effectiveness as an allergen barrier. Tests such as Pore Size, Use Simulation, Air Flow Panel and Air and Moisture permeability are performance based tests and provide an indication of the products effectiveness as an Allergen Barrier.
- Fabric Pore Size - The pore size of a fabric is the measurement of the air space between the fibers of the fabric or in the case of a membrane type barrier, perforations in a material. Only a small area of a fabric is tested with the sample size being about 1.75" - 2.25" in diameter. A very specialized piece of equipment is used for this type of test. A wetting liquid is used to fill the fabric pores and a pressurized gas is then used to displace the liquid. The gas pressure and flow rates through wet and dry samples are accurately measured. From the measured gas pressure and flow rates, the pore diameters and distribution can be calculated. A fabric can claim to be an effective allergen barrier if the tested mean pore size is below 10 microns in size (1 micron = 0.00003937 inch). Although the average size of a dust mite is 250 - 300 microns in size, the allergy and asthma trigger allergen is actually the fecal matter of the dust mite that has a size of 10-40 microns. Therefore, studies have shown that allergen barriers with a mean pore size below 10 microns begin to be effective at reducing the dust mite allergens from penetrating through the barrier.
- Use Simulation - This type of test tries to duplicate the activity of sleeping on an allergen barrier where constant human movement occurs. The barrier fabric is placed between two vials. One vial is empty and the other vial is loaded with the Dust Mite allergen and two small 1/8" steel ball bearings. The vials are rotated at 25 rotations per minute for 18 hours and the steel bearings mix with the allergen and pound on the fabric between the vials. At the completion of the rotation time period, the vial that was initially empty is tested for allergen content to determine how much allergen passed through the allergen barrier fabric.
- Air Flow Panel - Similar to pore size testing, this type of test can check on the tightness of construction of the allergen barrier fabric. A fabric sample of 8" x 8" is used. One side of the allergen barrier fabric is exposed to pressurized air at a constant air flow rate. A dust sample with know amounts of allergens is pulled across the fabric. A filter cassette is mounted downstream from the fabric to collect any allergens that may have penetrated through the fabric. The filter cassette is then tested to determine the amount of allergen that has passed through the allergen barrier fabric.
- Air and Moisture Permeability - In this analysis, the test is only determining how much air passes through the fabric at a given air pressure and how much moisture vapor is transmitted through the fabric over time. No allergens are used in this analysis. It provides a result that serves as a guideline as to how air permeable and moisture permeable a fabric is and from this information manufacturers determine if it is an acceptable level for their product.
- Comfort Modeling - This analysis takes the air and moisture permeability testing to another level to determine if the allergen barrier fabric will provide human comfort when used. A very specialized piece of equipment is used to create a "Skin Model" that simulates the way the skin emits heat and moisture (perspiration). Temperature, humidity and air movement can all be controlled in an air chamber to characterize the thermo-physiological quality of the allergen barrier material. The Skin Model is based on significant research and has lead to the formation of international standards ISO 11092 and EN 31092.
A consumer needs to be educated on what is important in buying an Allergen Barrier for pillows and mattresses. These products are a long term investment and making the right purchasing decision will provide both effective protection and long term durability, resulting in value. The goal of the consumer is to purchase an allergen barrier that is as effective as possible, is comfortable to use and will last a long time before needing replacement. As indicated below, certain characteristics of allergen barriers will impact their effectiveness, comfort and long term use. What follows are some general guidelines and information needed for a consumer to make a purchasing decision and understand the various claims being made by product manufacturers.
Fabric - there are several fabric options when considering an allergen barrier. Should you choose all cotton, polyester, polyester blend with cotton, a non-woven material such as polypropylene or a membrane or coated fabric type material? Here are some comments on the material options:
- Cotton - Cotton fibers range in length from 1/2" to 2". These short fibers are joined together by twisting to produce "spun" yarns which are then used to weave fabric. Over time, these short cotton staple fibers detach from the yarn and the yarn begins to break down and weaken. This can be seen in the lint screen of the clothes dryer every time cotton is laundered. As these cotton fibers break away from the yarn, the yarns become smaller on the fabric and the space between the yarns, the pore size, will become bigger. This is not desirable for allergen barrier material as increased pore size means reduced allergen protection. The breakdown of the cotton fiber means the long term durability of the fabric is reduced. Many 100% cotton allergen barrier products only carry up to a 5 year warranty and this is the reason why. Being a cellulosic fiber, Cotton is prone to mildew in moist environments. Each night, the human body releases over 8 ounces of perspiration creating the moist environment needed for mildew growth. Mildew digests cellulose and may cause holes over time in cotton fabric. Cotton also shrinks when washed which means the product is manufactured larger than needed to accommodate for shrinkage. Shrinkage can vary depending on how a customer launders the product. This means a product may fit loose when initially purchased and getting a proper fit to the mattress may or may not happen over time. A loose fit may cause uncomfortable creases under your sheets or cause your sheets to slide around on top of the mattress.
- Polyester - Filament yarns of Polyester are made from synthetic fibers through an extrusion process. This allows the individual filament fibers to be of very long length and grouped together with a slight twist to form a filament yarn. Filament yarns have no protruding ends or short fibers so they do not breakdown and lint like Cotton and filament yarns resist pilling. Polyester is very durable and has excellent abrasion resistance. Unlike Cotton, Polyester will not absorb moisture. Any moisture is wicked along the outer surface of the Polyester fibers to the fabric surface where it evaporates. Polyester fabric is also naturally resistant to biological attack such as mold, mildew and rot. Unlike Cotton, Polyester fabric is resistant to natural degradation and will have a longer usable life than natural fibers such as Cotton. Polyester allergen barriers are made to size and do not shrink with laundering. They provide the correct fit right out of the package and over the life of the product. We believe Polyester is the best choice for Allergen Barrier fabric and will provide years of effective protection.
- Non-Woven Fabric - Fabrics made from fibrous webs are called non-wovens. Short fibers of a specific material are laid down in a random order and bonded together by mechanical entanglement, using resins or by thermal fusion. These fiber webs are inexpensive to produce. The most common non-woven fabric used for allergen barriers is called "melt-blown" and is usually made from polyolefin. These fabrics tend to be stiffer and may be noisy as you move and less comfortable under your sheets. Durability can vary depending on types of fibers used and the manner in which they bonded together.
- Membranes and Coatings - Membrane films and coatings are not durable enough to stand on their own so they are laminated to fabric to provide structure. The most common fabric coating and membrane material is Polyurethane. Many of the membrane type allergen barriers indicate they are moisture permeable, but these products also claim to be water resistant or water proof. If a product won't allow moisture to penetrate through the barrier, how can it claim it has good moisture permeability? This is important for sleep comfort because each of us loses 8 ounces of liquid vapor a night while we sleep. Coated and membrane type allergen barriers are not very moisture permeable, meaning they can be hot and clammy to sleep on. Membrane and coated allergen barriers can be noisy to sleep on as they are more rigid or less flexible than non membrane material. This can also be disturbing to your sleep. The coatings and membrane chemicals can give off an odor that can be problematic to people with chemical sensitivities. When you sleep on a membrane or coated type allergen barrier pillow encasement, your nose is right on the product. Do you want to fall asleep to the smell of Polyurethane? Do you know the potential health impact of breathing the chemicals released by these products? Be watchful for products with membranes and coatings. Many manufacturers are not stating their products use a membrane or coating. One website of a membrane type barrier provides this description "uses 100% micro denier polyester fabric that is so tightly woven...". We believe this is misleading to the consumer as it implies the allergen barrier is only a woven fabric and it is never stated on the website that a coating is used and what that coating is. Look for descriptions of water resistance or waterproof as the first indicator of a membrane or coated fabric product, ask questions and look for the test data of moisture permeability.
Product Testing - Consumers need to be confident that the product they are purchasing is effective as an allergen barrier. Product testing is needed to demonstrate effectiveness of an allergen barrier fabric to the consumer. There are a variety of possible tests, each by themselves provide one aspect of an allergen barriers performance. We believe that multiple tests need to be performed to indicate the many characteristics of the allergen barrier for comfort and effectiveness. such as fabric pore size, air and moisture permeability, use simulation and They are an investment and need to provide years of comfort and durability.
- Pore size - testing for average pore size is important, but is not indicative of overall performance or comfort of an allergen barrier. Moisture permeability is important as well as the construction of the product. What good is a low pore size if it is uncomfortable to sleep on or the seams and zippers let allergen through. The pore size test provide the mean or average pore size of a sample of fabric. This means some pores will be larger than the average and some smaller. The lower the average pore size means the less there are larger pores in the fabric and the more there are smaller ones. For example, with a pore size average of 10 microns, there will be pores above this average rating, a level considered to be ineffective at trapping dust mite allergens. Obviously, there are levels of effectiveness and other considerations when thinking about pore size of an allergen barrier. The fecal matter of the dust mite maybe 10 microns initially, but as we move on our beds, this matter may break down to smaller sizes. Other allergens such as cat dander allergens are smaller, at 1-20 microns with an average size of 2.5 microns. So look for products with low pore size ratings.
- Moisture Permeable - very important for comfort because the greater the moisture permeability, the better the possible evaporation of moisture form the sleeper's body. As discussed earlier in fabric types, membrane laminates and coated fabrics are waterproof or water repellant and are not good at moisture permeability which can make these products hot and uncomfortable to sleep on. Unless you need a water repellant product, look for effective non-laminated and uncoated allergen barriers for the best comfort. Air and moisture permeability test results may be difficult to interpret unless provided on a scale. The Skin Model test duplicates the properties of the human skin in a sleep environment. Air and moisture permeability are determined and a classification is given ranging from "Not Sufficient to "Very Good". The Skin Model provides a way for the judgment of the physiological quality of allergen barriers and provides an easy to understand classification of the result for the consumer.
- Use Simulation - this test is rigorous in that it uses small ball bearings to repeatedly pound allergens against the barrier fabric to see what will come through to the other side. A good indicator of what can happen as the allergen barrier is used. This test primarily uses the Dust Mite allergen and does not use the smaller Cat allergen in testing.
- Air Flow Panel - a very important test to determine the effectiveness of an allergen barrier when allergens are forced against the fabric under air pressure. Anything that passes through is then measured to quantify the amount. There are options in the types of Allergens that are tested as well as what parts of the allergen barrier that is tested. Most companies test only the larger Dust Mite allergen, but test with the smaller Cat allergen show greater allergen protection. Most companies only test the fabric with an Air Flow Panel test, although areas such as seams and zippers can be tested as well. Look for products that test the smaller Cat allergens and also test the zippers and seams for effectiveness.
Quality of Construction - how an allergen barrier is made and the material and components used can provide a good indicator of the effectiveness and long term durability of the product.
- The zipper coil or "chain" is the long part the zipper glides on to open and close the encasement. The strength of the coil is important to ensure the zipper chain does not pull apart and the barrier becomes useless. The zipper itself must function well over repeated use. Look for name brand zipper components that mean quality.
- Seams should be covered and reinforced. This provides additional protection against allergen penetration and long term durability and strength. Look for products that use an additional layer of allergen barrier fabric to reinforce the seams. Some companies place their seams on the outside of the allergen barrier. this makes them unprotected and subject to abrasion. Look for products with seams on the inside of the barrier, this also provides a nicer appearance under your sheets.
- Stitching is important to the durability of the product. If a product uses a type of stitch that can unravel when any one of the stitches is broken, then the product will fall apart over time and loose it's effectiveness. Look for products that use the lockstitch method that won't unravel.
- Thread type can affect the useful life of the product and can be the weak link in long term durability. Natural fiber such as Cotton in a thread will eventually break down due to the fact that Cotton naturally degrades and is made from small fibers that are twisted to together to make the thread. These small fibers can fall off and weaken the thread over time and repeated launderings. Synthetic thread is better because it is stronger than Cotton threads, it does not breakdown and has good chemical resistance. Look for all synthetic thread, preferably with a monofilament core, for higher strength and durability.
- Additional Construction details such as inside flaps behind zippers and outside flaps to cover zippers help with appearance and performance of the allergen barrier. Placing a flap over the zipper coil on pillow encasements provides greater comfort for the head when placed over this area. Locking zippers that do not open unless pulled are another little detail that keeps zippers closed when they should be.
Place of Manufacture and Environmental Impact - Where a product is made has a big impact on the global environment and human rights. Many overseas countries do not have the same stringent environmental regulations and human rights as the USA. This is one reason for the decline of the textile industry in America. Because foreign manufacturing companies can operate with less stringent environmental regulations and labor controls, their costs are lower and the lower product price becomes appealing to companies that only concern themselves with providing cheaper products. Many foreign countries do not have the same air and water pollution control measures and hazardous waste disposal regulations as the America. Labor regulations, if any, in foreign countries don't always allow for fair compensation for the work that is performed resulting in "sweatshop" type working conditions of long hours at low pay. The US textile industry uses good operating practices to ensure that fabrics are made without excess chemicals, water and energy to minimize environmental impact. Hazardous waste disposal is closely monitored by the US Environmental Protection Agency (EPA) and State Departments of Environmental Protection (DEP). Made in America also means that the workers involved with all aspects of the production of the finished product were compensated fairly and the working conditions allow for dignity in the workplace according to the US Department of Labor and the Occupational Safety and Health Administration (OSHA). In a time of global environmental concern and US economic decline, look for products with fabric and assembly Made in the USA to support American workers and businesses.
Warranty - Allergen barriers are an investment. You want your allergen barrier to last for years of use without a problem. As discussed in the fabric section, Cotton allergen barriers may only have a 1-5 year warranty due to the inherent nature of natural fibers degrading over time. Look for a long term warranty in an allergy barrier with a simple replacement or return policy.
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