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What Decatizing Actually Does to Tweed<\/h2>\n
Decatizing (sometimes spelled “decatising” in British English) passes the fabric through a steam chamber and then wraps it around a perforated cylinder under tension. Steam penetrates the fiber, relaxing the internal stresses that built up during weaving. The wool or blend fibers swell, the yarn crimp redistributes, and the weave structure settles into its equilibrium position. After decatizing, the fabric is dried in position on the cylinder, which locks in the new dimensions.<\/p>\n
The key parameters are steam pressure (typically 2\u20134 bar for wool tweed), cylinder rotation speed (8\u201315 m\/min), and the number of passes. A single pass gives light relaxation \u2014 enough to remove most residual shrinkage but leave the fabric with a fairly natural hand. Two passes with higher pressure produce a fuller, softer fabric with more surface bloom, which is what premium suiting buyers expect. At a 300-loom mill, a standard decatizing cycle for 1,000 meters of 350 GSM tweed takes about 45 minutes.<\/p>\n
The measurable outcome is residual shrinkage. A properly decatized wool tweed should show less than 1.5% shrinkage in both warp and weft when tested under ISO 3759 (relaxation) and ISO 3760 (relaxation and relaxation-wet). If a buyer receives fabric that shrinks more than 2%, the mill either skipped decatizing or ran it too lightly. This is one of the most common quality disputes in woven fabric trade.<\/p>\n
Crabbing: Setting the Weave Structure<\/h2>\n
Crabbing is a different operation, though it’s often done on the same machine line. In crabbing, the fabric passes through a hot water trough (85\u201395\u00b0C for wool) and then wraps tightly around a large-diameter cylinder while under controlled tension. The hot water opens the wool fiber scales, and the tension on the cylinder forces the warp and weft yarns into their final positions within the weave. When the fabric cools on the cylinder, the fiber scales close again, locking the yarns in place.<\/p>\n
The purpose of crabbing is not just shrinkage control \u2014 it’s weave stability. A crabbed fabric resists skewing (also called spirality or bowing), which is the tendency of weft yarns to shift diagonally across the fabric width. Skewing is especially problematic in patterned tweeds like herringbone or houndstooth, where even a 2% skew is visually obvious. Crabbing also improves the fabric’s dimensional stability during garment manufacturing: a crabbed fabric holds its shape better when cut, pressed, and handled on the production floor.<\/p>\n
There are two types: single-crabbing (one pass through the hot water and cylinder) and double-crabbing (two passes, with the fabric rewound between passes so that both faces get equal treatment). Double-crabbing is the standard for premium suiting fabrics because it produces a more uniform set across the full fabric width. Single-crabbing is acceptable for coating and heavier tweeds where surface uniformity is less critical.<\/p>\n In a production finishing line, the order matters. Crabbing comes first, then decatizing. The logic is straightforward: crabbing sets the yarn positions in the weave under high tension and hot water; decatizing then relaxes the fibers and removes any residual shrinkage without disturbing the set that crabbing achieved. If you reverse the order \u2014 decatize first, then crab \u2014 the high-tension crabbing step can partially undo the relaxation that decatizing provided, and the fabric ends up with internal stress that shows up as shrinkage later.<\/p>\n A typical finishing sequence for a 350 GSM wool tweed destined for suiting looks like this: singe \u2192 crab (double) \u2192 decatize (two passes) \u2192 press \u2192 inspect. Each step adds cost and time \u2014 roughly USD 0.15\u20130.25 per meter for the combined crabbing and decatizing operations \u2014 but it’s a small fraction of the total fabric price and it eliminates the most common quality complaint.<\/p>\n For lighter-weight tweeds (under 280 GSM), some mills skip crabbing entirely and rely on decatizing alone. This works for plain weaves where skewing is less of a risk, but it’s a cost-cutting move, not a technical decision. If you’re sourcing patterned tweed \u2014 especially herringbone or other directional patterns<\/a> \u2014 insist on double-crabbing in your specification.<\/p>\n When you receive a bulk order, the first check is dimensional stability. Cut a 50 cm \u00d7 50 cm sample, mark it, steam it for 30 seconds with a standard hand press at 150\u00b0C, and measure the change. Warp shrinkage should be under 1.5%, weft under 1.5%. If it exceeds 2%, the finishing was inadequate.<\/p>\n The second check is skewing. Lay the fabric flat and measure the angle of the weft yarns relative to the selvedge. For a crabbed fabric, skew should be under 2%. For an uncrabbed fabric, 3\u20135% is common and may cause problems in garment cutting. The test method is standardized \u2014 ASTM International<\/a> publishes D3882 for measuring bow and skewness in woven and knitted fabrics, and most third-party inspection houses in China and Vietnam run it as part of pre-shipment inspection.<\/p>\n In your RFQ, specify the finishing sequence explicitly: “double-crabbed + two-pass decatized” for suiting-weight tweed, or “single-crabbed + one-pass decatized” for coating-weight. Don’t just write “finished” \u2014 that term means different things to different mills. Some mills consider a light steam pass to be “finishing,” while others run the full sequence. If you\u2019re building a tweed program and want the finishing spec written into the contract before sampling, send us the target weight and end-use<\/a> and we\u2019ll confirm the standard finishing route and price band. The 4-point inspection system<\/a> catches surface defects but won’t catch inadequate finishing \u2014 that requires separate shrinkage and skew testing.<\/p>\n For brands that run multiple fabric programs across different mills, standardizing the finishing specification is one of the highest-leverage quality controls available. A fabric that is properly crabbed and decatized at the mill will behave predictably in the garment factory, regardless of which cutting or pressing equipment is used downstream. For more on how weaving parameters<\/a> interact with finishing to determine final fabric quality, see our technical guide on tension and beat-up settings.<\/p>\n![\"Fabric](\"https:\/\/fursone.com\/wp-content\/uploads\/2026\/05\/fabric-defect-inspection-process-overview-scaled.webp\")
<\/figure>\nThe Correct Sequence: Crab First, Then Decatize<\/h2>\n
What Buyers Should Test and Specify<\/h2>\n
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