ASTM D7811 Bow & Skew Measurement Testing for Woven Fabrics
ASTM D7811 is used to determine the bow and skew of woven and knitted fabrics over a fixed distance using a measuring tool. The method is satisfactory for acceptance testing of commercial samples. The SI units should be considered as standard.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM D7811 describes a standard test method for measuring bow and skew in woven and nonwoven fabrics using a measuring tool. Bow refers to the curvature of filling yarns (or cross-direction rows) relative to the selvage, while skew refers to the angular deviation of filling yarns from a true perpendicular to the warp direction. Both are fabric distortion defects that affect cut-and-sew accuracy, pattern alignment, and product appearance.
This test is essential for textile quality control in apparel, technical textiles, and technical nonwovens where fabric distortion affects garment fit, seam alignment, and performance.
Scope, Applications, and Benefits
Scope
ASTM D7811 evaluates:
- Bow percentage in woven and nonwoven fabrics
- Skew percentage and angular deviation
- Filling yarn or cross-direction row curvature
- Compliance with bow/skew tolerance specifications
Applications
- Apparel and fashion fabric quality control
- Upholstery and home furnishing fabric inspection
- Technical textile and geotextile bow/skew measurement
- Nonwoven web quality assessment
- Textile finishing process control (heat setting, tentering)
Benefits
- Standardized measurement using a defined measuring tool
- Quantifies bow and skew for specification compliance
- Identifies process issues in weaving, finishing, or tentering
- Enables supplier qualification for bow/skew-sensitive applications
- Applicable to both woven and nonwoven fabrics
Test Process
Specimen Conditioning
Fabric specimens are conditioned at 21 °C and 65% RH for a minimum of 4 hours before measurement.
1Fabric Layout
The fabric is laid flat on a smooth, level surface without tension; the selvage or fabric edge is aligned along a straight reference line.
2Bow / Skew Measurement
Using the ASTM D7811 measuring tool, the maximum deviation of filling yarns or cross-direction rows from a straight line perpendicular to the selvage is measured at the mid-panel and edge positions.
3Calculation & Reporting
Bow (%) = (maximum deviation / fabric width) × 100; Skew (%) = (deviation at the selvage / fabric width) × 100. Results are reported against specification tolerances.
4Technical Specifications
| Parameter | Details |
|---|---|
| Applicable Materials | Woven fabrics, nonwovens, knitted fabrics |
| Measured Properties | Bow (%), Skew (%) |
| Conditioning | 21 °C ± 2 °C, 65% ± 4% RH |
| Measurement Tool | ASTM D7811 specified bow/skew gauge |
| Typical Tolerance | Bow ≤3%, Skew ≤3% (application dependent) |
Instrumentation Used for Testing
- ASTM D7811 bow/skew measuring tool
- Level, smooth inspection table
- Steel ruler and marking chalk
- Environmental conditioning room
- Digital protractor (for angular skew measurement)
Results and Deliverables
- Bow percentage value
- Skew percentage value
- Pass/fail determination against specification tolerance
- Measurement location documentation
- Full test report per ASTM D7811
Frequently Asked Questions
Bow is a curved distortion of filling yarns across the fabric width — they arc toward or away from the center. Skew is a diagonal distortion where filling yarns run at an angle to the warp, rather than perfectly perpendicular. Both are distortions but of different geometric types.
Bow and skew are primarily introduced during wet finishing, heat setting, and tentering operations where uneven tension, misaligned clip chains, or differential drying rates distort the fabric structure. They can also originate from loom or nonwoven machine alignment issues.
Distorted fabric causes misalignment of patterns and stripes during cutting, leading to twisted seams, mismatched patterns, and poor garment fit. Even small bow/skew percentages can cause significant aesthetic defects in striped or patterned garments.
Mild bow and skew can be partially corrected by controlled re-tentering, finishing, or steam relaxation. However, severe distortion may be irreversible in finished fabrics, making early detection and process control essential.
Most apparel fabric specifications require bow ≤2–3% and skew ≤2–3%. Technical textile applications may have tighter or looser tolerances depending on end-use requirements. Striped and plaid fabrics typically have tighter limits than plain fabrics.
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