T-Shirt Jargon Can Be Expressed Like This

T-Shirt Jargon Can Be Expressed Like This

While browsing fabric markets, knowledgeable people might inquire about a T-shirt with questions such as: "What's the CPI of this T-shirt? What's the machine gauge E? Has the yarn feed length been adjusted?" Now, let's delve into these three questions by focusing on CPI (Courses Per Inch), Machine Gauge E, and Yarn Feed Length/Stitch Length.

1. CPI (Courses Per Inch): A Core Parameter Determining T-shirt Weight, Feel, and Function

CPI (Courses Per Inch, i.e., the number of courses per inch) is one of the key indicators measuring the tightness of knitted fabric structures, directly reflecting the number of courses contained within a unit distance along the length of the fabric. For an ordinary cotton T-shirt, CPI not only determines its weight (GSM) but also profoundly affects the smoothness of the fabric surface, drape, elastic recovery rate, and wearing comfort.

Typically, T-shirts are made using single jersey construction. Under identical yarn counts (e.g., 32S cotton yarn) and machine gauges (e.g., E28), increasing CPI from 50 to 65 means adding 15 more courses per inch, compressing loop height, making the fabric denser and crisper, and potentially increasing GSM by 15–25 g/m². Conversely, if CPI is low (e.g., 45 CPI), loops are loose, edges curl easily, the fabric feels soft but lacks body, suitable for loose casual styles; whereas high CPI (e.g., 70+) is common in premium basics or sports T-shirts, emphasizing wrinkle resistance and shape retention.

It's important to note that CPI is not determined by machine hardware but rather by adjusting stitch cam position (bend depth) and take-down tension. The same E28 circular knitting machine can produce both lightweight 40 CPI summer T-shirts and thick 80 CPI fleece fabrics—depending on the coordination between yarn feeding and take-down systems. Therefore, asking about the CPI (“What's the CPI of this T-shirt?“) essentially probes into the process settings rather than the equipment itself. Precise control over CPI is the technical foundation for achieving design intents such as “lightweight and breathable” or “dense and structured.”

2. Machine Gauge E: The Fundamental Architecture of T-shirt Manufacturing, Limiting Yarn Choices and Fabric Fineness

The question "What's the machine gauge E?" touches upon the hardware basis of knitting production. E (such as E24, E28, E32) represents the number of needles per inch around the circumference of the needle cylinder on a circular knitting machine, which is an inherent physical attribute of the equipment and cannot be changed during production unless the needle cylinder is replaced. It serves as the foundation, fundamentally limiting the minimum loop size, applicable yarn count range, and fabric fineness.

For example:

E24 Machines: With larger needle pitches (approximately 1.06 mm), they suit coarser cotton yarns (16S–21S), resulting in thick, textured fabrics often used for workwear T-shirts or vintage-style products.

E28 Machines: The industry standard, compatible with fine combed cotton (26S–32S), balancing efficiency, cost, and quality, producing smooth-surfaced, moderately weighted standard T-shirts.

E32/E36 Machines: With finer needle pitches (E32 pitch ≈ 0.79 mm), they require high-count cotton or blended yarns (above 40S), yielding extremely fine, drapey fabrics used in premium brands' basics or close-fitting undergarments.

It’s crucial to understand that machine gauge E does not directly equate to fabric density. An E32 machine could still produce looser fabric (lower CPI/WPI) if the process is loosened. However, E value sets a limit—E24 machines cannot achieve the ultra-fine surface effects possible with E32 machines due to physical constraints on minimum loop size. Thus, when designers request “very fine fabric,” the technical department first checks if they have E32 or higher gauge machines. In essence, machine gauge E is the "ceiling" for T-shirt quality, while CPI/WPI are the means through which processes reach this ceiling.

3. Yarn Feed Length: The Invisible "Knitting Code," Controlling Loop Shape and Fabric Performance

The question "Has the yarn feed length been adjusted?" addresses one of the most subtle yet critical variables in knitting processes. Yarn feed length (typically measured in millimeters per revolution, mm/rev) refers to the amount of yarn fed into the looping system per revolution of the circular knitting machine. Though not directly visible on the finished fabric, it acts like "invisible DNA," determining the geometric shape of loops, yarn tension distribution, and ultimately the physical properties of the fabric.

In T-shirt production, yarn feed length works alongside CPI and WPI to form a "process triangle":

Increasing yarn feed length (feeding more yarn) results in larger, looser loops, reducing CPI and WPI, making the fabric softer, lighter, and more elastic but prone to deformation and puckering.

Decreasing yarn feed length (feeding less yarn) tightens loops, increasing CPI and WPI, making the fabric denser, heavier, and more stable in size but harder and less breathable.

What is yarn feed length? For example, a yarn feed length of “110 mm/rev” means 110 millimeters of yarn fed per feed per machine revolution (i.e., 11 centimeters per feed per revolution).

T-shirts are made from single jersey fabric, knitted on a single-knit circular knitting machine. With each machine revolution, one course (horizontal row) is formed. Each course consists of N loops, where N equals the total number of needles. The yarn feed length (e.g., 110 mm/rev) represents the length of yarn consumed per loop. The term “mm/rev” is a process-specific expression: it was initially established as a standard and has since been gradually adopted and become a conventional industry practice.

The calculation is as follows: If the yarn feed length = 110 mm/rev (i.e., 110 mm of yarn per loop), and the machine is a single-knit circular knitting machine with a 30-inch cylinder and E28 gauge (approximately 2,640 needles), then: Total yarn consumption per revolution = 110 mm × 2,640 ≈ 290 meters. Although this figure may seem large, it is consistent with the actual yarn consumption of high-speed circular knitting machines.

For instance, using an E28 machine and 32S cotton yarn to knit a T-shirt:

If the yarn feed length is set at 110 mm/rev, you might get a typical style with 58 CPI, 26 WPI, and 160 GSM.

If adjusted to 125 mm/rev, it could result in a lighter version with 50 CPI, 22 WPI, and 135 GSM, better suited for summer wear.

If excessively reduced to 95 mm/rev, although you could achieve 70 CPI, excessive yarn tension might lead to yarn breakage, shiny fabric ("mirror effect"), and even damage to needles or cams.

Imagine a string of beads (loops) strung on a thread (fabric lengthwise):

If each bead is tall (more yarn fed), only 50 beads fit in one inch, so CPI = 50.

If beads are compressed (less yarn fed), 70 beads fit in one inch, so CPI = 70.

With less yarn fed and fixed machine speed, loops (the basic ring-shaped structure formed by knitting needles, the smallest unit of knitted fabric, known as loop/stitch in English) become smaller and tighter. When forcibly stretched both horizontally and vertically to the same dimensions, fabrics with fewer yarn feeds may appear similarly dense compared to those with more yarn feeds, but: Fabrics with less yarn feed require greater force to stretch to the same size and will quickly rebound to their original compact state once released. Fabrics with more yarn feed are prone to permanent deformation or edge curling.

An analogy:

A brick wall.

"Smaller bricks" correspond to smaller loops.

"more layers of bricks per meter" correspond to increased CPI.

"a layer of bricks" ≈ a course.

"a brick" ≈ a loop.

Cases of insufficient yarn feed. If the yarn feed length is excessively reduced (e.g., forcefully set to a very low value):

Excessive yarn tension can cause yarn breakage.

Loops deform, leading to shiny fabric ("mirror effect").

Elasticity is lost, making the fabric stiff.

Even needles or cams may be damaged.

Thus, yarn feed length must strike a balance between yarn strength, machine capability, and fabric appearance.

Additionally, yarn feed length must dynamically match the angle of the stitch cam, sinker pressure, and take-down speed. Modern electronic yarn feeders can achieve ±0.1 mm precision closed-loop control, ensuring uniform fabric density across the entire bolt. Therefore, whether the yarn feed length has been adjusted not only concerns individual samples but also impacts batch production stability and consistency. It is the most sensitive "tuning knob" in the hands of process engineers, where slight adjustments of a few millimeters can transform a T-shirt from "loose and limp" to "crisp and structured."

Conclusion (Summary of the Relationships Among the Three):

CPI, machine gauge E, and yarn feed length represent the process outcomes, hardware platform, and process control in T-shirt manufacturing, respectively.

Machine gauge E is the "stage"—setting the boundaries for performance.

Yarn feed length is the "director"—dictating how yarn forms loops.

CPI is the "performance"—what the audience sees as the final product.

Only through the synergistic optimization of these three factors can ideal T-shirts be produced, meeting both aesthetic designs and functional requirements.