Wool and PET
Fibers for Rugs
Most rugs today are made from synthetic fibers, about half as many are made from wool, and the remainder are made with various other natural fibers such as cotton, jute and silk. (These estimates are based on market value; actual numbers of rugs are harder to come by, but a good estimate is that roughly two-thirds are synthetic, roughly one-fifth wool, and roughly one-tenth are made with other natural fibers.
Catherine Bertulli Carpets primarily makes rugs in wool and PET, a synthetic. We work with mills that can use some of the other synthetic and natural fibers, but wool —specifically New Zealand wool — and PET make up most of our orders.
Wool
New Zealand wool is considered the best choice for custom rugs. It is a clean white, wool, which allows for both clear pastel dyes and deep black ones. It resists flattening under furniture (this is called “crimp memory”), and is strong and durable. Starting in 20026, we have noticed a tightness in the supply of NZ Wool, which is due to a combination of declining numbers of sheep used for wool and increased demand — China currently buys about 85% of the NZ wool crop. There are many other sources for wool, including British, Tibetan, Himalayan, and Australian Merino; some of these are “nearly as good” as NZ wool, while others excel in particular characteristics. In general, wool is considered to be the “gold standard” both for its qualities and its long history – the oldest known designed wool rug dates to the 4th century BCE.
PET
PET (Polyethylene Terephthalate) is a premium, eco-friendly fiber made from 100% recycled plastics (primarily plastic water bottles and other post-consumer containers). For custom rugs, PET offers an excellent combination of sustainability, performance, and beauty. It is particularly well-suited for homes with children, pets, or busy lifestyles, where easy cleaning and durability matter. It is also well-suited for outdoor or indoor-outdoor applications. There are two primary ways to dye PET. Pressure dying and solution dying.
In pressure dying, the PET fibers are mixed with the dye under high pressure an temperature. The heat expands the PET fibers, creating spaces between that trap the particles of dye. The entire process takes about 3 hours for one batch
An alternative for dying PET is called “solution dying” or “dope dying”. With this method, the color is added to the mix of chemicals before that mixture is drawn into yarns. Solution-dyed PET is not typically used for custom rugs because a mill would to have to purchase much larger amounts of yarn, in each color, than would be needed for any one rug.
Why Choose Wool?
Wool is soft and luxurious under foot. It is naturally resilient and durable. It holds dye well. While the colors can fade with continued exposure to strong UV light, the existence of many “oriental” rugs that are hundreds of years old testifies that if these rugs are protected from strong UV their colors will show minimum fading over a long life. Wool can also become brittle after exposure to strong UV Light.
Wool has some stain-resistant qualities, but it can absorb water-based stains. There are treatments that can greatly enhance a wool rugs stain and dirt resistance, but they may not provide much protection against acids, dyes or bleach. Wool also has some natural flame resistance.
A PET rug on an uncovered deck, after two years.
Why Choose PET?
PET can feel indistinguishable from wool. Pressure-dyed PET is less sensitive than wool to strong sunlight (although solution-dyed PET is even less sensitive). PET is moisture resistant and hence shows good resistance to stains.
It is the case that some poorly processed pressure-dyed PET can have, on the molecular level, what are called “empty dye sites:” If the dyeing process isn’t perfect, or if the fiber’s chemistry makes it hard for dye to fully penetrate, you can end up with molecular sites that don’t get fully occupied. Such sites can absorb stains. The best way to determine if this is likely to be a problem is to ask your mill (or have your Designer ask) if they have lab test results from organizations like AATCC (American Association of Textile Chemists and Colorists), ISO (International Standards Organization) or the Indian NABL (National Accreditation Board for Testing and Calibration Laboratories).
If your mill has no certifications but you and your designer still want to use them, you can also do an informal test; we’d recommend doing these tests on a sample (either the one made for your rug or one that the Designer has previously had made). Begin by placing a small drop of water in an inconspicuous part of the rug, wait 1-2 minutes and then blot. If the water barely sinks in and wipes cleanly the rug is likely to be stain resistant. After this first test you can repeat with a small drop of staining liquid (dilute tea, juice or coffee). After waiting 1-2 minutes blot with a clean damp cloth and mild detergent. If it blots leaving little or no mark, it is likely that open dye sites will not be a problem with this rug.
Wool or PET: How to Choose
If staining or outdoor usage are not an issue, you will probably be well-served by either wool or PET; rely on your Designer to help you decide. You might give an edge to wool as the safe, conventional choice or, if comparing samples made with wool and PET, you prefer the look or feel of wool. Consider PET for outdoor or indoor/outdoor areas, like a mud room, or where staining is likely, such as kitchen or dining room rugs.