A polyester knitted fabric roll may have the correct GSM, DIA, colour and surface finish, yet still contain thin vertical lines running continuously along its length.
These lines may look like scratches, narrow streaks, gaps or slight variations in the knitted texture.
In circular-knitted fabric production, some of these defects are known as needle lines and sinker lines.
Unlike sewing needle damage, which occurs during garment stitching, these defects can originate inside the knitting machine while the fabric itself is being manufactured.
For polyester fabric manufacturers, knitting technicians and bulk garment buyers, understanding these defects is important because they can affect fabric appearance, printing quality, cutting efficiency and garment acceptance.
This article explains what needle lines and sinker lines are, how they develop, how to distinguish them and how manufacturers can prevent them.
1. What Is a Needle Line in Knitted Fabric?
A needle line is a visible lengthwise mark or wale irregularity associated with abnormal loop formation at one or more knitting needles.
Circular knitting machines contain hundreds or thousands of needles arranged around a needle cylinder.
Each needle plays a role in forming knitted loops.
When a needle is damaged, worn, incorrectly positioned or unable to operate properly, the loops formed at that position may differ from neighbouring loops.
This difference can create a continuous line in the fabric.
Depending on the defect, a needle line may appear as:
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A narrow vertical streak.
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An unusually open or tight wale.
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A line of irregular knitted loops.
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A fine gap in the fabric structure.
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A repeated line of distorted stitches.
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A visible surface irregularity after dyeing.
The line generally follows the wale direction of the knitted fabric.
Why Does a Needle Line Continue Along the Fabric Length?
In circular knitting, each needle repeatedly forms loops as the machine operates.
If a particular needle consistently produces abnormal stitches, the defect can continue through successive fabric courses.
As a result, one faulty needle can create a visible line extending through a considerable length of fabric.
This is why a seemingly small machine defect can affect a large quantity of production.
2. What Is a Sinker Line in Knitted Fabric?
A sinker line is a lengthwise fabric irregularity associated with abnormal sinker operation or the condition of sinker-related knitting components.
Sinkers are important elements in many circular knitting machines.
Depending on machine design, they help control yarn and fabric during loop formation, holding down existing loops and assisting stitch formation.
If a sinker becomes damaged, worn, incorrectly positioned or unable to move correctly, it can disturb the knitting process.
This may produce a visible line or structural irregularity in the fabric.
Sinker-related defects may appear as:
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Fine lengthwise streaks.
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Uneven loop formation.
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Local differences in fabric texture.
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Narrow lines of irregular stitches.
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Variations in loop appearance.
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Repeated surface marks.
However, not every vertical line is a sinker line.
Similar-looking defects can also result from needles, yarn variation, machine settings or finishing processes.
Correct identification requires examination of the knitted structure and machine components.
3. Needle Lines vs Sinker Lines: What Is the Difference?
Both defects can create visible lengthwise marks in knitted fabric.
However, their mechanical origins are different.
| Feature | Needle Line | Sinker Line |
|---|---|---|
| Main origin | Abnormal needle operation | Abnormal sinker operation |
| Component involved | Knitting needle | Sinker |
| Primary effect | Irregular loop formation at a needle position | Disturbance of loop holding or formation |
| Appearance | Lengthwise wale irregularity | Lengthwise structural or surface irregularity |
| Common causes | Bent, worn or damaged needles | Worn, damaged or poorly moving sinkers |
| Corrective focus | Needle and associated mechanism | Sinker and associated mechanism |
Visual appearance alone may not be sufficient to identify the exact cause.
Knitting technicians often inspect both the fabric and machine before deciding which component is responsible.
4. How Do Needles and Sinkers Work in Circular Knitting?
To understand these defects, it is useful to understand the basic circular knitting process.
A circular knitting machine produces fabric by forming interconnected yarn loops.
The main elements include:
Needles: Form and release knitted loops.
Sinkers: Assist yarn and loop control in machine designs that use them.
Yarn feeders: Deliver yarn to the knitting elements.
Cams: Control the movement of needles and, where applicable, sinkers.
Take-down system: Pulls the knitted fabric away from the knitting zone under controlled tension.
These components must operate in a coordinated sequence.
If one component behaves differently from the others, the resulting loop structure may become inconsistent.
Over thousands of machine rotations, even a small mechanical problem can create a repeated defect.
5. Major Causes of Needle Lines in Polyester Knitted Fabric
5.1 Bent Knitting Needles
A bent needle may not follow its intended path correctly.
This can affect yarn catching, loop formation and stitch release.
The resulting fabric may contain distorted or uneven stitches along the affected wale.
Needles can become bent because of mechanical impact, excessive stress or improper handling.
5.2 Worn Needle Hooks
The needle hook is responsible for capturing and manipulating yarn during stitch formation.
As needles operate repeatedly, their surfaces can experience wear.
A damaged or worn hook may interfere with normal yarn handling.
This can produce inconsistent loops or other knitting defects.
5.3 Damaged Needle Latches
Many circular knitting machines use latch needles.
The latch opens and closes during the knitting cycle.
If the latch is damaged, obstructed or unable to move freely, the needle may fail to form stitches correctly.
Depending on the failure, the fabric may develop irregular loops, dropped stitches or other defects.
5.4 Incorrect Needle Movement
Needle movement is controlled through the machine's cam system.
If the needle cannot move through its required path, stitch formation may be affected.
Possible contributing factors include:
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Damaged needle butts.
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Incorrect cam settings.
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Mechanical obstruction.
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Worn needle tracks.
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Poor lubrication.
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Contamination.
These problems can create repeated structural irregularities.
5.5 Needle Contamination
Textile knitting machines operate continuously and may accumulate:
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Yarn lint.
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Fibre fragments.
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Dust.
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Oil residues.
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Processing deposits.
If contamination interferes with needle movement, the knitting action can become inconsistent.
Regular cleaning helps maintain reliable operation.
5.6 Incorrect Needle Replacement
Replacing a damaged needle with an incompatible component may create differences in loop formation.
Needles should match the machine manufacturer's specifications.
Using an incorrect needle type, gauge or geometry can produce defects or damage the knitting mechanism.
6. Major Causes of Sinker Lines in Polyester Knitted Fabric
6.1 Worn Sinkers
Sinkers experience repeated mechanical contact during knitting.
Over time, their working surfaces can wear.
A worn sinker may handle the yarn or fabric differently from neighbouring sinkers.
This can create a repeated structural variation.
6.2 Damaged Sinker Noses
The sinker nose or other working surfaces can influence loop control.
If these surfaces become chipped, bent or worn, they may disturb stitch formation.
The resulting defect depends on the machine design and extent of damage.
6.3 Incorrect Sinker Movement
Sinkers must move according to the intended machine sequence.
If a sinker becomes obstructed or cannot travel correctly, the fabric structure may be affected.
Possible causes include:
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Mechanical wear.
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Incorrect settings.
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Dirt accumulation.
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Damaged components.
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Inadequate lubrication.
6.4 Sinker Contamination
Lint, oil residues and other deposits can accumulate around moving knitting components.
This may restrict movement or create inconsistent mechanical contact.
Regular maintenance is therefore important.
6.5 Incorrect Sinker Replacement
Using an incompatible sinker can affect the operation of the knitting machine.
Replacement components should match the required specifications and be installed correctly.
6.6 Excessive Mechanical Wear
Continuous high-speed knitting places repeated demands on machine components.
Poor maintenance or operation outside suitable conditions can accelerate wear.
As wear increases, the risk of knitting defects may also increase.
7. Why Are Needle and Sinker Lines Sometimes More Visible After Dyeing?
A grey polyester fabric may contain minor structural irregularities that are difficult to notice before processing.
After dyeing and finishing, these irregularities may become more visible.
This can happen because differences in loop geometry influence:
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Surface texture.
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Light reflection.
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Fabric coverage.
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Local density.
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Visual shade perception.
For example, a slightly more open wale may reflect light differently from surrounding areas.
After the fabric is dyed a dark solid colour, the difference may appear as a noticeable vertical streak.
However, dyeing does not necessarily create the original defect.
In many cases, it simply makes an existing structural problem easier to see.
It is also important to distinguish mechanical knitting lines from actual dye streaks, which can have different causes.
8. Why Are These Defects Important in Polyester Fabric?
Polyester knitted fabrics are widely used for garments where surface consistency matters.
Examples include:
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Sportswear.
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Dry-fit T-shirts.
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Polo shirts.
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School uniforms.
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Corporate uniforms.
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Casualwear.
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Activewear.
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Sublimation-printed jerseys.
Visible needle or sinker lines can reduce the appearance and commercial acceptability of the finished fabric.
In plain-coloured garments, the defect may remain visible across the chest, back or sleeves.
In printed garments, the line may still be noticeable through the design, especially when it creates a structural or reflective difference.
9. Which Polyester Knitted Fabrics Can Develop Needle Lines?
Needle-related defects can occur in many knitted constructions.
Single Jersey
Single jersey is widely used for T-shirts and lightweight apparel.
Its relatively smooth surface can make lengthwise streaks easier to notice.
Piqué Fabric
Piqué contains a characteristic textured structure.
Needle irregularities may disturb the consistency of the pattern.
Interlock Fabric
Interlock uses a double-knit construction.
Mechanical defects can affect loop formation and the uniformity of the surface.
Polyester-Lycra Fabric
Stretch fabrics require consistent loop formation and yarn handling.
Defects may become more visible when the material is stretched.
Honeycomb and Mesh Fabrics
These constructions contain structured surface patterns or openings.
Mechanical knitting problems can disturb the regularity of the pattern.
Bird-Eye Fabric
Bird-eye constructions contain repeated small texture elements.
Needle or sinker problems can interrupt the uniformity of the knitted design.
The exact defect appearance depends on the knitting-machine type, yarn and fabric construction.
10. Needle Lines vs Barré Marks: Are They the Same?
No.
Needle lines and barré marks may both affect fabric appearance, but they commonly have different characteristics.
| Feature | Needle Lines | Barré Marks |
|---|---|---|
| Typical direction | Lengthwise | Crosswise |
| Common appearance | Vertical streaks | Horizontal bands |
| Common origin | Needle-related loop irregularity | Yarn, feeder, knitting or dye-affinity variation |
| Detection | Fabric and machine inspection | Fabric, yarn-lot and process investigation |
| Prevention | Needle and machine maintenance | Yarn consistency and process control |
Direction can be a useful initial clue, but it is not a complete diagnosis.
Some defects may resemble one another, and fabric orientation during inspection must be considered.
For a detailed explanation of barré, read our article on Barré Marks in Polyester Knitted Fabric.
11. Needle Lines vs Sewing Needle Damage
These defects should not be confused.
Knitting needle lines originate during fabric manufacture.
Sewing needle damage occurs during garment stitching.
Sewing needle damage may produce:
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Broken yarns near seams.
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Holes along stitch lines.
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Local yarn displacement.
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Damage caused by unsuitable sewing needles.
Knitting needle lines, by contrast, can extend continuously along the fabric before it is cut into garment panels.
This distinction helps manufacturers identify which production stage requires corrective action.
12. How Can Fabric Inspectors Identify Needle and Sinker Lines?
Fabric inspection should be performed under suitable lighting and controlled conditions.
Step 1: Open the Fabric
Inspect a representative length of fabric rather than relying on a small folded sample.
Step 2: Identify the Direction
Determine whether the mark follows the wale direction, course direction or another path.
Step 3: Examine the Loop Structure
Use suitable magnification to inspect the knitted loops.
Look for:
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Irregular loop size.
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Missing or distorted stitches.
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Abnormal wale spacing.
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Surface damage.
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Repeated structural differences.
Step 4: Compare Adjacent Wale Columns
Check whether the affected region differs from neighbouring areas.
Step 5: Record the Defect
Document its location, appearance, frequency and affected fabric length.
Step 6: Inspect the Knitting Machine
If the defect is traced to production, examine the relevant needles, sinkers and associated mechanisms.
A consistent machine-position defect can help technicians narrow down the source.
13. Can Needle and Sinker Lines Be Removed During Finishing?
The answer depends on the defect.
Some minor appearance differences may become less noticeable after suitable finishing.
However, severe mechanical knitting defects are generally difficult to eliminate once the fabric has been produced.
If the defect involves:
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Missing stitches.
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Permanently distorted loops.
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Broken yarns.
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Structural gaps.
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Repeated mechanical damage.
Finishing cannot reliably reconstruct the original knitted structure.
Attempting additional processing may also introduce new quality risks.
Prevention during knitting is therefore the preferred approach.
14. How Knitting Mills Can Prevent Needle Lines
Regular Needle Inspection
Inspect needles for wear, bending and mechanical damage.
Replace Defective Needles
Replace damaged needles using components that match machine specifications.
Maintain the Cam System
Ensure the needle movement mechanism operates correctly.
Control Lubrication
Follow the machine manufacturer's lubrication requirements.
Clean the Knitting Zone
Remove accumulated lint and contamination.
Monitor Fabric During Production
Inspect fabric at appropriate intervals to identify defects early.
Maintain Production Records
Record recurring defects and component replacement history.
These practices help reduce repeated quality problems and unnecessary fabric waste.
15. How Knitting Mills Can Prevent Sinker Lines
Preventive measures include:
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Inspecting sinkers regularly.
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Replacing worn or damaged sinkers.
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Checking sinker movement.
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Maintaining suitable lubrication.
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Removing lint and deposits.
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Verifying correct component specifications.
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Monitoring fabric appearance during knitting.
Preventive maintenance is particularly important in machines operating continuously for high-volume fabric production.
16. Why Early Detection Can Save Large Quantities of Fabric
Consider a circular knitting machine producing polyester fabric continuously.
If a needle becomes damaged and the machine continues operating, the same defect may repeat throughout the production run.
A defect that could have been corrected through a relatively small maintenance intervention may eventually affect many kilograms of fabric.
This can result in:
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Fabric downgrading.
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Additional inspection.
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Reduced cutting efficiency.
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Rejected garment panels.
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Production delays.
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Customer complaints.
The exact financial impact depends on the defect severity, fabric value and production quantity.
Regular in-process inspection is therefore an important part of quality control.
17. Do Needle and Sinker Lines Affect Fabric Strength?
Not every needle or sinker line reduces fabric strength.
Some defects primarily affect appearance.
However, defects involving damaged yarns, missing loops or weakened knitted structures may affect mechanical performance.
For example, a line containing repeated damaged stitches may create a locally weak region.
The impact should be evaluated according to the defect type and intended garment application.
A visual inspection alone may not establish whether the fabric meets the required strength specification.
18. What Should Bulk Fabric Buyers Check?
When purchasing polyester knitted fabric in bulk, buyers should consider more than GSM, DIA and colour.
Useful inspection questions include:
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Does the fabric contain visible lengthwise streaks?
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Are the knitted loops consistent?
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Are the marks structural or only visual?
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Do the defects appear throughout the roll?
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Are multiple rolls affected?
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Has the fabric been inspected after dyeing and finishing?
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Does the defect exceed the agreed quality acceptance criteria?
For critical applications, buyers may request representative fabric samples or inspection reports before bulk dispatch.
19. Why Fabric Quality Cannot Be Judged by GSM Alone
GSM measures the mass of fabric per square metre.
It does not directly measure knitting-machine performance or loop consistency.
Two polyester fabrics can have identical:
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GSM.
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DIA.
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Colour.
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Fibre composition.
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Nominal yarn specifications.
Yet one fabric may contain visible needle lines while the other has a uniform surface.
This demonstrates why quality inspection must include structural and visual evaluation.
Fabric specifications describe important material properties, but they do not guarantee freedom from manufacturing defects.
20. Frequently Asked Questions
What causes vertical lines in polyester knitted fabric?
Vertical lines may result from damaged needles, sinker problems, yarn variation, machine settings or finishing-related effects. The knitted structure should be examined to determine the actual cause.
Are needle lines and sinker lines the same?
No. Needle lines are associated with abnormal needle operation, while sinker lines are associated with sinker-related problems. Their appearance can sometimes be similar.
Can needle lines appear after dyeing?
Yes. Structural irregularities may become more visible after dyeing because of differences in surface texture and light reflection.
Can needle lines be removed by washing?
Severe structural needle lines generally cannot be reliably removed through ordinary washing.
Are needle lines common in single jersey fabric?
Needle-related defects can occur in single jersey and other knitted constructions. The smooth surface of some single jersey fabrics can make streaks more noticeable.
Do needle lines affect sublimation printing?
They can. Structural irregularities may remain visible after printing, particularly when they affect surface texture or light reflection.
Can a single damaged needle affect an entire fabric roll?
Yes. A defective needle can repeatedly produce abnormal stitches until the underlying problem is corrected.
How can knitting mills prevent sinker lines?
Regular sinker inspection, component replacement, cleaning, lubrication and machine maintenance can help reduce sinker-related defects.
Are all vertical fabric streaks knitting defects?
No. Some streaks may originate from yarn variation, dyeing, finishing or other processes. Proper investigation is necessary.
Conclusion
Needle lines and sinker lines are important technical defects in polyester knitted fabric manufacturing.
Although they may appear as small vertical marks, they can affect the appearance, consistency and commercial value of finished fabric.
Needle lines are generally associated with abnormal needle operation, while sinker lines originate from problems involving sinkers or related mechanisms.
Both highlight the importance of knitting-machine maintenance, consistent loop formation and regular fabric inspection.
For garment manufacturers and bulk fabric buyers, understanding these defects helps identify potential quality problems before cutting and stitching.
At Walrus – Yes India Can, we supply a wide range of polyester knitted fabrics for sportswear, T-shirts, uniforms, casualwear and garment manufacturing.
Explore our fabric collections and contact our team for bulk sourcing requirements.
Website: https://www.yesindiacan.in/
Contact: +91 90420 77722
