The 4-Point Inspection System: How a Fabric Lot Gets Approved
How 4-point fabric inspection works under ASTM D5430 — defects scored 1-4 by size, a cap of 4 points per linear yard, normalised to 100 yd², and common acceptance thresholds — together with the in-house lab gate that completes it (ISO 105 fastness, ISO 3801 weight, ISO 6330/5077 dimensional stability, spectrophotometer ΔE).
Before it ships, a fabric lot passes two independent gates. The first is a visual-surface gate: the fabric runs across a back-lit inspection table while every defect is scored by its size — this is the industry-standard 4-point system (ASTM D5430). The second is the in-house lab gate, which measures the engineering properties you cannot see — colour, weight, fastness, dimensional stability. The first tells you whether the fabric's surface is clean; the second tells you whether the fabric meets its specification. No roll is approved until both are cleared.
How the 4-Point System Works
The inspector runs the fabric across a back-lit table, typically at around 15-18 m/min, flagging every knitting/weaving fault or stain. It is the defect's longest dimension, not its type, that sets the score: a small fault scores 1 point, a medium one 2-3, a large one 4. Holes count as 4 points outright, regardless of size. Two rules keep the system honest: no single linear yard can be assigned more than 4 points (a dense cluster can't inflate the total), and across the width a single row is also capped at 4 points.
Raw points are then normalised to a common base — 100 square yards — so a narrow roll and a wide roll can be compared fairly. The formula is simple: total points are multiplied by 100 and divided by the inspected area in square yards. The result is the lot's single numeric quality grade: defect points per unit area.
| Defect size (longest dimension) | Points assigned |
|---|---|
| Up to 3 in (~7.5 cm) | 1 point |
| Over 3 in – 6 in (~7.5–15 cm) | 2 points |
| Over 6 in – 9 in (~15–23 cm) | 3 points |
| Over 9 in (~23 cm+) | 4 points |
| Hole / tear (any size) | 4 points |
| Cap per linear yard | 4 points max |
The Acceptance Threshold: How Many Points "Pass"
The normalised score is compared against an acceptance limit. A common, general-purpose acceptance threshold across the industry is, representatively, around 40 points per 100 yd²: rolls below it are taken to pass, those above are rejected or set aside as seconds. For performance and premium work, buyers demand a tighter window — typically ~20-28 points per 100 yd². These figures are contractual thresholds, not absolute law: the final limit is always agreed between buyer and supplier for the end use. The 4-point system supplies the neutral shared language; the parties set the threshold.
The Second Gate: The In-House Lab
A clean surface does not mean the right fabric. In parallel with visual inspection, an in-house lab running accredited methods verifies the lot's measurable properties. This guarantees that what is promised on the fabric's TDS (technical data sheet) matches what is delivered — especially in 100% polyester knits, because weight, shrinkage and colour are ultimately locked in at the dyehouse and the stenter (heat-setting frame).
- Colour / ΔE: the sample is read on a spectrophotometer against the approved lab-dip standard; the typical target is ΔE ≤1.0 (CMC or CIEDE2000), often under multiple illuminants to catch metamerism. This aligns with standard colour-management practice (see our ΔE / colour-management guide).
- Fastness (ISO 105 series): resistance to washing (C06), light (B02), rubbing/crocking (X12), and the sublimation/heat fastness (P01) that is critical for synthetics. Disperse dyeing of polyester needs reduction clearing for fastness in dark shades (see our reductive-clearing / disperse-dyeing guides).
- Weight (ISO 3801 / ASTM D3776): mass per unit area (g/m²); the core commercial spec of a knit, the joint result of gauge·stitch length·yarn count (see our weight-map guide).
- Dimensional stability (ISO 6330 wash + ISO 5077 / AATCC 135 measurement): percent dimensional change after a standard wash-dry cycle; the typical commercial target for knits is ~3-5% shrinkage, under 3% for premium. Spirality/skew (AATCC 179) is checked here too.
- Additional performance tests (where applicable): bursting/breaking strength (ISO 13938 / ASTM D3786), pilling and abrasion (ICI/Martindale), DWR spray rating (ISO 4920) — by end use.
Why This Is Stronger at a Single-Roof Producer
In a plant where knitting, dyeing and finishing sit under one roof, the inspection gate stands at the end of the chain rather than in the middle: a single lot number linking the greige roll to the dyed batch ties the visual score and the lab data into the same traceability record. Because the same lab runs both the lab-dip approval and the bulk dye bath, colour consistency improves structurally. This is the same integrated control that raises the right-first-time (RFT) rate, reduces re-dyeing, and makes GRS chain-of-custody documentation straightforward for recycled polyester. The 4-point number and the lab ΔE are therefore not separate promises but two measures of a single quality story.