Rug people throw around terms like “KPSI,” “abrash,” and “overcast edge” like everyone grew up on a loom floor. Here’s what they actually mean.
Whether you’re shopping for a rug, talking to an appraiser, or just trying to understand what your cleaner meant by “browning,” rug terminology gets specialized fast. This glossary breaks down the real vocabulary of rug construction, fiber, dye, damage, and cleaning in plain language, organized by category so you can find what you need.
Quick answer: Rug terminology falls into a few clear categories: construction (how a rug is made — pile, knots, warp/weft, foundation), fiber and dye (what it’s made of and how it’s colored), pattern and design (motifs and style names), and condition or care terms (damage types and cleaning methods). Knowing these terms helps you evaluate quality, describe problems accurately, and understand what a cleaner or appraiser is telling you.
Construction Terms
Pile is the visible surface layer of a rug — the yarn tufts or loops that stand up from the foundation and give the rug its texture, thickness, and cushioning underfoot.
Knot count (KPSI) stands for knots per square inch, a measure of how densely a hand-knotted rug is woven. Higher KPSI generally means finer detail, more weaving hours, and higher quality — a coarse rug might run 40-80 KPSI, while a fine one can exceed 200.
Warp and weft are the two thread systems that form a rug’s foundation. Warp threads run the length of the rug and are strung on the loom first; weft threads run crosswise, woven between the warps to lock the structure together as knots are tied.
Foundation refers to the warp-and-weft base a rug’s pile is knotted or tufted into. A stable foundation — usually cotton, wool, or occasionally silk — is what gives a rug its shape and long-term durability.
Fringe vs. selvedge: fringe is the exposed warp thread at a rug’s short ends, left after weaving; selvedge is the reinforced, often overcast edge running along the rug’s long sides. People often call both “fringe,” but they’re structurally different and wear differently.
Hand-knotted, machine-made, and hand-tufted describe three different production methods with very different value. Hand-knotted rugs are woven knot-by-knot on a loom, often over months. Machine-made rugs are produced on power looms with synthetic fiber, quickly and uniformly. Hand-tufted rugs are punched by hand through a fabric backing using a tufting gun, then glued and sheared — faster than hand-knotting but not as durable, since the backing can separate over time.
Overcast edge is a finishing technique where yarn is wrapped tightly around a rug’s side edge to prevent the foundation from unraveling. A damaged or unraveling overcast edge is one of the most common repair issues we see.
Fiber Terms
Wool is the most common rug fiber, prized for durability, natural soil resistance, and the ability to hold up to deep, full-immersion washing without losing structure.
Silk is a luxury fiber known for its sheen and fine detail, but it’s more delicate than wool, more sensitive to sunlight and abrasion, and requires gentler handling during cleaning.
Viscose (sometimes marketed as “art silk” or “rayon”) is a semi-synthetic fiber made from processed plant cellulose. It mimics silk’s shine at a lower cost but is notably weaker when wet and prone to permanent watermarking if not handled correctly.
Wool-blend rugs combine wool with synthetic or cotton fibers to reduce cost or add specific properties like stain resistance, but blends can clean and age differently than 100% wool depending on the ratio.
Dye & Color Terms
Natural dye vs. synthetic dye: natural dyes come from plants, roots, insects, or minerals and were standard before the mid-1800s; synthetic (aniline or chrome) dyes dominate production today. Natural dyes tend to fade and mellow gracefully with age, while synthetic dyes can fade more unevenly or bleed if not properly set.
Colorfastness describes how well a dye resists running or fading when exposed to water, light, or cleaning agents. Testing colorfastness before any wet cleaning is a critical first step, since a non-colorfast dye can bleed into surrounding fibers.
Abrash refers to subtle, natural color variation within a single dye lot of hand-spun, hand-dyed wool — visible as faint horizontal banding in the field of a rug. Far from a flaw, abrash is considered a hallmark of genuine hand craftsmanship.
Pattern & Design Terms
Kilim is a flat-woven rug made without knots or pile, produced by interweaving colored weft threads directly into the warp. Kilims are lighter, reversible, and structurally different from pile rugs in how they should be cleaned and handled.
Medallion pattern refers to a large, often symmetrical central design element — frequently a diamond, oval, or star shape — anchoring the middle of a rug’s field, a hallmark of many traditional Persian and Oriental rug designs.
Damage & Wear Terms
Moth damage refers to destruction caused by carpet moth larvae, which feed on keratin — the protein in wool and other animal-hair fibers — leaving irregular bare patches or holes. Synthetic fibers aren’t a food source for moths, which is one reason wool rugs need more vigilant storage care.
Uric acid crystals are the residue left behind by pet urine after it dries. They’re a major cause of yellowing, odor, and dye damage, and because they’re not water-soluble once crystallized, they require specialized treatment beyond ordinary spot cleaning.
Browning is a yellow-to-brown discoloration that appears in natural-fiber and some wool rugs when cellulose-based components get over-wetted and don’t dry quickly enough, causing natural sugars to oxidize at the surface.
Cleaning & Care Terms
Full-immersion wash is a deep-cleaning method where a rug is completely submerged and washed on all sides, flushing soil, allergens, and residue out of the base of the pile — the gold standard for wool and silk rugs.
Dry dusting is a mechanical process, usually done before wet cleaning, that vibrates or beats dry soil and grit out of a rug’s foundation. Skipping this step and going straight to wet cleaning can turn dry soil into mud within the pile.
Centrifuge extraction is a controlled spin process used after washing to remove excess water from a rug quickly and evenly, shortening drying time and reducing the risk of browning, shrinkage, or mildew.
Tip: If a cleaner or appraiser uses a term you don’t recognize, ask them to explain it in plain language before agreeing to any service. Understanding what’s actually happening to your rug — not just the price — is the best way to make sure it’s handled correctly.
Why This Vocabulary Actually Matters
Knowing these terms isn’t just trivia. When you can describe a problem accurately — “the selvedge is unraveling” instead of “the edge is messed up,” or “I think there’s uric acid staining” instead of “there’s a weird yellow spot” — you get faster, more accurate answers from whoever is helping you. It also helps you evaluate quality when buying a rug, since knot count, fiber type, and dye method are the actual drivers of a rug’s durability and value, not just its size or color. And when it comes to cleaning, understanding methods like full-immersion washing versus dry dusting helps you ask the right questions about how your specific rug — wool, silk, viscose, or natural fiber — should be handled.
Frequently asked questions
What’s the difference between fringe and selvedge?
Fringe is the exposed warp thread at a rug’s short ends; selvedge is the reinforced edge binding along its long sides. They’re different structural elements and often need different repair approaches.
Is a higher knot count always better?
Generally yes for fineness of detail and weaving skill, but knot count alone doesn’t determine value — fiber quality, dye type, age, and condition all factor in too.
What does abrash mean and is it a defect?
Abrash is natural color banding from hand-dyed wool, not a defect. It’s actually considered a sign of authentic handcraft rather than something to avoid.
Why does my rug’s cleaner talk about “colorfastness testing”?
Colorfastness testing checks whether a rug’s dyes will bleed or run when exposed to water or cleaning solution. It’s a standard first step before any wet cleaning method is chosen.
Can moth damage be reversed?
No — moth larvae destroy the keratin fibers they feed on, and that loss is permanent. Damaged areas need professional repair (reweaving or patching), not cleaning, to restore them.
What’s the difference between hand-tufted and hand-knotted?
Hand-knotted rugs are woven knot-by-knot on a loom and can last generations. Hand-tufted rugs are punched through a backing with a tufting gun and glued in place — faster to produce but generally less durable over time.
Do you clean rugs made from any of these fiber types?
Yes, we clean wool, silk, viscose, cotton, and natural-fiber rugs, choosing the method — full immersion or a specialty low-moisture approach — based on the specific fiber and construction.
Get a Free Quote → (469) 429-RUGS(7847)
Related: professional rug cleaning · our cleaning methods · Oriental rug cleaning