Fabric Parameters: Understanding the Basic Construction of Woven Fabric
A woven fabric may look simple from the outside, but its behaviour is controlled by a few important constructional parameters. These parameters decide how compact, heavy, soft, firm, transparent, flexible, or durable a fabric will be. For a merchandiser, designer, weaver, buyer, or textile student, understanding these parameters is essential because they form the language through which fabric quality is described.
In woven fabrics, the most important basic parameters are ends per inch, picks per inch, yarn count, crimp, and weave structure. Apart from these, fabric weight, cover factor, and thickness are also important when one has to evaluate or compare fabrics technically.
Table of Contents
- Basic Woven Fabric Parameters
- Ends Per Inch and Picks Per Inch
- Yarn Count
- Crimp in Fabric
- Weave or Fabric Structure
- Fabric Weight
- Cover Factor
- Fabric Thickness
- Practical Importance for Merchandisers
- Related Reading
- General Disclaimer
1. Basic Woven Fabric Parameters
There are four basic constructional parameters that are essential for describing almost every woven fabric. These are ends per inch and picks per inch, yarn count used in warp and weft, crimp in warp and weft yarns, and weave or fabric structure.
These four parameters are interconnected. A change in one parameter usually affects the others. For example, if the EPI and PPI are increased without changing the yarn count, the fabric becomes more compact. If the yarn becomes coarser, the same construction may become heavier and stiffer. If the crimp changes, the fabric weight, handle, and dimensional behaviour may also change.
| Parameter | Meaning | Practical Effect on Fabric |
|---|---|---|
| EPI | Number of warp yarns per inch | Affects width-wise density, cover, strength and appearance |
| PPI | Number of weft yarns per inch | Affects length-wise density, compactness and fabric feel |
| Yarn Count | Fineness or coarseness of yarn | Affects weight, thickness, drape and handle |
| Crimp | Bending of yarn due to interlacement | Affects cover, elongation, shrinkage and softness |
| Weave | Arrangement of warp and weft | Affects texture, strength, drape and surface effect |
2. Ends Per Inch and Picks Per Inch
Ends per inch, or EPI, refers to the number of warp yarns present in one inch of fabric width. Picks per inch, or PPI, refers to the number of weft yarns present in one inch of fabric length. Together, EPI and PPI describe the thread density of the fabric.
The usual method of determining thread density is by using a pick glass or fabric counting glass. The fabric is placed under the glass, and the number of warp and weft threads in a fixed area is counted. In many fabric specifications, EPI and PPI are written together in the form:
\[ EPI \times PPI \]
For example, a fabric construction written as \(74 \times 66\) means that the fabric has 74 ends per inch and 66 picks per inch. This construction gives a first-level idea of how closely the fabric is woven, but it does not by itself explain the complete fabric character.
Balanced Construction
A fabric is sometimes called balanced when the number of warp yarns and weft yarns per inch are nearly equal. However, balance should not be judged only by EPI and PPI. Yarn count, yarn diameter, crimp and weave structure also influence whether a fabric behaves in a balanced manner.
For example, a fabric may have almost equal EPI and PPI, but if the warp yarn is much finer than the weft yarn, the fabric may not look or behave as truly balanced. Therefore, construction balance must be understood in relation to yarn size and fabric structure.
3. Yarn Count
Yarn count expresses the fineness or coarseness of yarn. In fabric construction, the yarn count of both warp and weft is important because it directly affects fabric weight, thickness, cover, strength and handle.
In the tex system, yarn count represents the weight in grams of 1000 metres of yarn. Therefore:
\[ Tex = \frac{\text{Weight in grams}}{\text{Length in metres}} \times 1000 \]
A higher tex value means a coarser or heavier yarn. A lower tex value means a finer yarn. If two fabrics have the same EPI and PPI but one uses coarser yarn, that fabric will generally be heavier, thicker and more compact.
4. Crimp in Fabric
Crimp refers to the waviness or bending of yarn caused by interlacement with yarns running in the opposite direction. In a woven fabric, warp yarns pass over and under weft yarns, and weft yarns pass over and under warp yarns. Because of this interlacement, the yarn path inside the fabric is not straight.
Crimp is calculated by comparing the length of yarn removed from the fabric with the length of fabric from which it was removed. If \(L_y\) is the length of yarn after removal and straightening, and \(L_f\) is the original length of fabric, then:
\[ Crimp = \frac{L_y - L_f}{L_f} \]
When expressed as a percentage:
\[ Crimp\% = \frac{L_y - L_f}{L_f} \times 100 \]
For example, if a yarn is removed from 1 metre of fabric and its straightened length is 1.08 metres, then:
\[ Crimp\% = \frac{1.08 - 1.00}{1.00} \times 100 = 8\% \]
Crimp values commonly fall within a broad range depending on fabric type, yarn type, construction, tension and weave. In many woven fabrics, crimp may range from low single-digit values to higher values such as 10 percent or more.
Why Crimp Matters
Crimp affects many fabric properties, including cover, thickness, softness, extensibility, shrinkage and hand feel. A fabric with higher crimp may feel fuller or softer, but it may also show higher dimensional changes during finishing or washing.
Crimp balance is also important. If the warp tension during weaving is high and the weft tension is low, the weft may develop more crimp while the warp remains comparatively straighter. Such imbalance can affect appearance, dimensional stability and wear behaviour.
5. Weave or Fabric Structure
Weave refers to the arrangement of warp and weft yarns in the fabric. It tells us how the warp and weft interlace with each other. The three fundamental weave families are plain weave, twill weave, and satin or sateen weave.
In plain weave, every warp yarn alternately passes over and under every weft yarn. This creates a firm and stable fabric structure. In twill weave, the interlacement pattern creates diagonal lines on the fabric surface. In satin and sateen weaves, longer floats create a smoother and often more lustrous surface.
The weave structure affects strength, drape, surface texture, abrasion behaviour, appearance and even the apparent compactness of the fabric. Therefore, two fabrics may have the same EPI, PPI and yarn count but behave differently because their weave structures are different.
6. Fabric Weight
Fabric weight is generally expressed as grams per square metre, or GSM. In a woven fabric, the total fabric weight is the sum of the weight contributed by warp yarns and weft yarns.
If \(W_1\) is the warp weight per square metre and \(W_2\) is the weft weight per square metre, then:
\[ Total\ Fabric\ Weight = W_1 + W_2 \]
Warp Weight Per Square Metre
The warp weight per square metre can be calculated as:
\[ W_1 = \left[n_1 \times 100 \times \frac{100 + C_1}{100}\right] \times \frac{N_1}{1000} \]
Where \(n_1\) is ends per cm, \(N_1\) is warp count in tex and \(C_1\) is warp crimp percentage.
Weft Weight Per Square Metre
Similarly, the weft weight per square metre can be calculated as:
\[ W_2 = \left[n_2 \times 100 \times \frac{100 + C_2}{100}\right] \times \frac{N_2}{1000} \]
Where \(n_2\) is picks per cm, \(N_2\) is weft count in tex and \(C_2\) is weft crimp percentage.
Piece Weight
Once the GSM is known, the weight of a fabric piece can be calculated as:
\[ Piece\ Weight = GSM \times Piece\ Length \times Piece\ Width \]
Here, length and width should be taken in metres. The final value will be in grams if GSM is used.
Example
Suppose a fabric is 120 metres long and 1.3 metres wide. It has 30 ends per cm of 12 tex warp and 24 picks per cm of 15 tex weft. The warp crimp is 5 percent and the weft crimp is 8 percent.
The fabric particulars can be written as:
\[ 30 \times 24;\ 12\ tex \times 15\ tex;\ 5\% \times 8\% \]
Warp weight per square metre:
\[ W_1 = \left[30 \times 100 \times \frac{105}{100}\right] \times \frac{12}{1000} \]
\[ W_1 = 37.8\ g/m^2 \]
Weft weight per square metre:
\[ W_2 = \left[24 \times 100 \times \frac{108}{100}\right] \times \frac{15}{1000} \]
\[ W_2 = 38.88\ g/m^2 \]
Therefore:
\[ GSM = 37.8 + 38.88 = 76.68\ g/m^2 \]
Now, piece weight:
\[ Piece\ Weight = 76.68 \times 120 \times 1.3 \]
\[ Piece\ Weight = 11962.08\ g \]
Therefore, the piece weighs approximately:
\[ 11.96\ kg \]
7. Cover Factor
Cover factor indicates how much of the fabric area is covered by yarns. It gives an idea of the closeness or compactness of the fabric construction. A higher cover factor generally means a more compact fabric, while a lower cover factor indicates a more open fabric.
Warp cover factor can be calculated as:
\[ K_1 = \frac{n_1 \times \sqrt{N_1}}{10} \]
Where \(K_1\) is warp cover factor, \(n_1\) is ends per cm and \(N_1\) is warp count in tex.
Similarly, weft cover factor can be calculated as:
\[ K_2 = \frac{n_2 \times \sqrt{N_2}}{10} \]
The total cover factor is:
\[ K = K_1 + K_2 \]
Example of Cover Factor
For a fabric with 30 ends per cm and 24 picks per cm, using 12 tex warp and 15 tex weft:
\[ K_1 = \frac{30 \times \sqrt{12}}{10} = 10.39 \]
\[ K_2 = \frac{24 \times \sqrt{15}}{10} = 9.30 \]
Therefore:
\[ K = 10.39 + 9.30 = 19.69 \]
8. Fabric Thickness
Fabric thickness is the distance between the upper and lower surfaces of the fabric under specified pressure. For many apparel fabrics, thickness may not be the first parameter used in buying specifications. However, it becomes very important in technical textiles, belts, felts, coated fabrics, interlinings, upholstery, blankets and performance fabrics.
Thickness affects warmth, cushioning, stiffness, handle, compressibility and bulk. Two fabrics may have the same GSM but different thickness because of differences in yarn type, weave, finishing and fibre characteristics.
9. Practical Importance for Merchandisers and Fabric Buyers
Fabric parameters are not merely academic terms. They are practical tools for fabric identification, costing, sourcing, quality checking and complaint analysis. A merchandiser who understands EPI, PPI, yarn count, crimp, weave, GSM and cover factor can communicate more accurately with mills, suppliers, designers, buyers and testing laboratories.
For example, if the fabric feels too light, one can check whether the issue is due to lower EPI, lower PPI, finer yarn count, reduced crimp or a change in width. If the fabric appears too open, the reason may lie in lower cover factor, finer yarn or an unsuitable weave. If the fabric shrinks more than expected, crimp and finishing history may need to be examined.
| Observation | Possible Parameter to Check |
|---|---|
| Fabric feels lighter than approved sample | GSM, EPI, PPI, yarn count and width |
| Fabric looks more open or transparent | Cover factor, yarn count, weave, EPI and PPI |
| Fabric has poor dimensional stability | Crimp, finishing, relaxation and yarn tension |
| Fabric feels stiff | Yarn count, construction density, finish and thickness |
| Fabric surface looks different | Weave, yarn type, crimp balance and finishing |
Conclusion
The basic parameters of woven fabric are like the grammar of fabric construction. Ends per inch and picks per inch define thread density. Yarn count defines the fineness or coarseness of yarn. Crimp explains how yarn behaves inside the fabric. Weave determines the interlacement pattern. Fabric weight, cover factor and thickness help us evaluate the final fabric more completely.
A good understanding of these parameters helps in fabric development, costing, quality control, sourcing and troubleshooting. Whether one is a student, merchandiser, designer or textile professional, these concepts form the foundation for understanding woven fabrics in a practical and technical way.
General Disclaimer
This article is intended for educational and practical understanding of woven fabric parameters. Formulae and examples are simplified for learning purposes. In industrial practice, actual fabric behaviour may vary depending on fibre type, yarn structure, loom settings, finishing treatments, testing conditions, moisture regain and measurement standards. For formal testing, commercial decisions or quality disputes, relevant textile standards and laboratory test methods should be followed.
