Determination of Fabric Stiffness
Fabric stiffness is one of the important properties that affects the handle, drape, appearance and end-use performance of a fabric. The Indian Standard IS 6490:1971 — Method for Determination of Stiffness of Fabrics: Cantilever Test gives a standard method for measuring fabric stiffness by allowing a fabric strip to bend under its own weight.
In simple terms, this test helps us understand whether a fabric is soft and limp, or firm, crisp and structured. A fabric that bends easily has low stiffness, while a fabric that resists bending has high stiffness.
Fabric stiffness is the resistance of a fabric to bending. It is closely related to fabric handle and drape, but it is not exactly the same as fabric weight. A light fabric can be stiff, and a heavy fabric can sometimes be soft and flexible depending on yarn, weave and finishing.
1. What This Standard Is About
IS 6490:1971 describes the cantilever test for determining the stiffness of fabrics. In this method, a fabric strip is placed on a horizontal platform and slowly pushed forward. As the fabric projects beyond the platform edge, it bends downward due to its own weight.
The length of the projecting fabric is measured when the fabric tip reaches a fixed inclined reference line. In this standard, the reference angle is:
\( 41.5^\circ \)
The test is suitable for many woven fabrics, but it is not very suitable for very limp fabrics or fabrics that curl or twist badly when cut into small strips.
2. Principle of the Cantilever Test
The principle of the test is simple. A rectangular strip of fabric behaves like a cantilever beam when it projects beyond the edge of a platform. The overhanging part bends under its own weight.
The more the fabric can project before bending to the reference angle, the stiffer the fabric is. A limp fabric bends quickly with a short overhang, while a stiff fabric requires a longer overhang before reaching the same angle.
In the cantilever test, a higher overhang length generally means higher stiffness. This is why crisp fabrics project further before bending, while soft and drapey fabrics bend earlier.
3. Important Terms
| Term | Meaning |
|---|---|
| Stiffness | Resistance of fabric to bending. |
| Bending length | A measure related to how far the fabric can project before bending under its own weight. |
| Flexural rigidity | Resistance of the fabric to bending by an external force. |
| Overall flexural rigidity | Combined bending behaviour considering both warpway and weftway directions. |
4. Why Fabric Stiffness Matters
Stiffness affects how a fabric behaves in use. It influences the way the fabric falls, folds, drapes, handles, sews and performs in the final product.
| Area | Effect of Stiffness |
|---|---|
| Drape | Stiff fabrics fall in larger, more angular folds; limp fabrics fall in soft folds. |
| Handle | High stiffness gives a firm or boardy feel; low stiffness gives a soft feel. |
| Garment appearance | Affects silhouette, fall, crispness and structure. |
| Sewing performance | Very limp fabrics may be difficult to control; very stiff fabrics may resist folding. |
| End use | Shirting, suiting, sarees, upholstery and technical fabrics require different stiffness levels. |
For example, a crisp cotton fabric may have a higher bending length than a soft voile. A coated denim may show greater stiffness than an ordinary denim fabric. A saree with low stiffness may fall softly, while one with higher stiffness may feel crisp and structured.
5. Test Specimens
The standard prescribes rectangular test specimens of:
\( 25 \times 200 \text{ mm} \)
Specimens are cut separately in the warpway and weftway directions. The lengthwise direction of the specimen should be parallel to the direction in which stiffness is to be measured.
While cutting the specimens, care should be taken to avoid:
- Selvedge areas
- End portions of the fabric
- Creased areas
- Folded places
- Damaged or distorted areas
Fabric stiffness may be different in warp and weft directions because yarn count, yarn twist, fabric density, weave structure and finishing may not be the same in both directions.
6. Conditioning and Testing Atmosphere
Before testing, fabrics should be conditioned to moisture equilibrium and tested under standard textile atmospheric conditions:
\( 65 \pm 2\% \text{ RH and } 27 \pm 2^\circ C \)
Moisture can affect fabric stiffness, especially in fabrics made from natural or moisture-sensitive fibres such as cotton, viscose, silk, wool and jute. Therefore, conditioning helps improve consistency of test results.
7. Apparatus Used
The apparatus used is a stiffness tester. It mainly consists of a horizontal platform, an inclined indicator and a graduated scale.
| Part | Requirement / Purpose |
|---|---|
| Horizontal platform | A smooth, flat, low-friction surface on which the specimen is placed. |
| Inclined indicator | Set at \(41.5^\circ\) below the platform plane to provide the reference bending angle. |
| Scale | Graduated scale used to move the specimen and measure the overhanging length. |
| Spirit level | Used to level the platform before testing. |
8. Procedure in Simple Words
- Place the stiffness tester on a stable table.
- Adjust the platform so that it is level.
- Place the fabric strip on the horizontal platform.
- Place the scale on top of the specimen.
- Keep the zero of the scale aligned with the leading edge of the fabric.
- Slowly push the fabric and scale forward together.
- The fabric begins to project beyond the platform edge and bends under its own weight.
- Stop when the tip of the fabric reaches the inclined reference line of \(41.5^\circ\).
- Measure the length of the overhanging portion.
- Repeat the test for both sides and both ends of the specimen as required.
If the specimen twists slightly, the centre of the leading edge may be used for observation. However, specimens that twist excessively should not be used for measurement.
9. Calculation of Bending Length
First, calculate the mean overhanging length \(L\), expressed in centimetres.
The bending length \(C\) is calculated as:
\( C = \frac{L}{2} \)
where:
\( C = \text{bending length in cm} \)
\( L = \text{mean overhanging length in cm} \)
For example, if the mean overhanging length is:
\( L = 4.8 \text{ cm} \)
then:
\( C = \frac{4.8}{2} = 2.4 \text{ cm} \)
Higher bending length means the fabric is stiffer and tends to drape more rigidly. Lower bending length means the fabric is more flexible and drapey.
10. Calculation of Flexural Rigidity
Flexural rigidity measures the resistance of the fabric to bending. It is calculated using:
\( G = W \times C^3 \)
where:
\( G = \text{flexural rigidity in mg-cm} \)
\( W = \text{weight per unit area of fabric in mg/cm}^2 \)
\( C = \text{bending length in cm} \)
Since \(C\) is cubed, even a small increase in bending length can produce a large increase in flexural rigidity.
Example
Suppose:
\( W = 20 \text{ mg/cm}^2 \)
\( C = 2.4 \text{ cm} \)
Then:
\( G = 20 \times 2.4^3 \)
\( G = 20 \times 13.824 \)
\( G = 276.48 \text{ mg-cm} \)
Therefore, the flexural rigidity of the fabric is:
\( 276.48 \text{ mg-cm} \)
11. Overall Flexural Rigidity
A fabric may have different stiffness in the warpway and weftway directions. Therefore, the standard gives a combined value known as overall flexural rigidity.
\( G_o = \sqrt{G_w \times G_f} \)
where:
\( G_o = \text{overall flexural rigidity} \)
\( G_w = \text{warpway flexural rigidity} \)
\( G_f = \text{weftway flexural rigidity} \)
12. Practical Interpretation of Results
| Result | Interpretation |
|---|---|
| Low bending length | Fabric is soft, limp, flexible and drapey. |
| High bending length | Fabric is stiff, crisp, structured or boardy. |
| Low flexural rigidity | Fabric bends easily. |
| High flexural rigidity | Fabric strongly resists bending. |
| Warpway stiffness > weftway stiffness | Fabric is stiffer along the warp direction. |
| Weftway stiffness > warpway stiffness | Fabric is stiffer along the weft direction. |
13. Factors Affecting Fabric Stiffness
Fabric stiffness is influenced by many fibre, yarn, fabric and finishing factors.
- Fibre type
- Yarn count
- Yarn twist
- Ends per inch and picks per inch
- Weave structure
- Fabric weight
- Finishing treatment
- Resin finishing
- Coating or lamination
- Calendaring
- Moisture content
A resin-finished cotton fabric may show higher stiffness than an unfinished cotton fabric. A tightly woven poplin may be stiffer than a loosely woven voile. Similarly, coated denim may show much higher flexural rigidity than ordinary denim.
14. What Should Be Reported?
A proper test report should include:
- Type of fabric tested
- Number of warpway specimens tested
- Number of weftway specimens tested
- Bending length in warpway direction
- Bending length in weftway direction
- Flexural rigidity in warpway direction
- Flexural rigidity in weftway direction
- Overall flexural rigidity, if required
- Any relevant observations such as curling, twisting or unusual fabric behaviour
Conclusion
IS 6490:1971 gives a practical and simple method for measuring fabric stiffness using the cantilever principle. The test connects laboratory measurement with real fabric behaviour such as handle, drape, crispness and structure.
Fabric stiffness is not only a laboratory value; it is one of the reasons why one fabric flows softly while another stands firm, crisp and structured.
Based on IS 6490:1971 — Method for Determination of Stiffness of Fabrics: Cantilever Test, Bureau of Indian Standards. Available at: Internet Archive PDF .
Goyal, P. How do we measure Stiffness of a fabric. My Textile Notes. Available at: http://mytextilenotes.blogspot.com/2026/05/how-do-we-measure-stiffness-of-fabric.html
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