How to interpret flannel fabric specifications?

In my 20 years of textile manufacturing, the most expensive mistake I see buyers make is sourcing flannel based on GSM alone.

⚠️ The “Summer Shirt” Disaster

🧬 Decoding the Equation

How to read a flannel fabric spec sheet is not just about checking one number. You must decode the interaction between:

• GSM (Weight)
• Yarn Count (Thickness)
• Density (EPI / PPI)
• Brushing Level (Loft)

✅ Your Technical Translator

This guide is your technical translator. We will move beyond the basics to help you predict warmth, pilling, and shrinkage directly from the spec sheet, ensuring your PO delivers exactly the fabric you envisioned.

The Standard List

A standard mill spec sheet typically lists the basics: Fiber Content, Weave, GSM, Width, Yarn Count, Density, and Finish.

⚠️ However, for flannel, the “Standard” sheet is often missing three critical elements:

1. Brushing Level & Side

Many sheets just say Brushed. They don’t specify if it’s single brushed flannel (one side) or double brushed. This changes the handfeel entirely.

2. Tolerances

What tolerances should be in a flannel spec sheet? Without them, a 150 GSM delivery against a 160 GSM order is “technically” acceptable to some mills. You must define the acceptable range (e.g., ±5%).

3. Test Methods

Shrinkage <3%” means nothing if you don’t specify the test. You must cite the standard, such as AATCC 135 (Dimensional Changes of Fabrics after Home Laundering).

GSM (Grams per Square Meter) measures mass, not warmth.

What GSM Tells You:

• Body/Drape: Heavier fabric falls straighter; lighter fabric drapes more.
• Opacity: Higher GSM generally means less see-through.
• Base Warmth: More material generally holds more heat, but brushing matters more.

⚠️ Why GSM Alone Is Misleading

✅ Suggested GSM Ranges by End-Use

• 👔 Shirts: 130 – 160 GSM (Light/Mid)
• 🛌 Pajamas: 140 – 170 GSM (Mid)
• 🛏️ Bedding: 160 – 190 GSM (Mid/Heavy)
• 🧣 Throws/Blankets: 200 – 300+ GSM (Heavy)

See detailed ranges in our Flannel Weight Guide

🧪 How to Verify GSM Quickly (Warehouse Method)

1. Cut a sample using a GSM Cutter (100cm² circle).
2. Weigh it on a digital scale (e.g., reads 1.60g).
3. Multiply by 100 = 160 GSM.

1. Yarn Count Basics

2. Ringspun vs Open-End vs Compact

• Open-End (OE): Cheaper, rougher, weaker. High pilling risk. Avoid for premium flannel.
• Ringspun: Standard for quality. Smoother, stronger.
• Compact: Premium. Lowest hairiness, lowest pilling.

3. Cotton vs Polyester Flannel Yarn

4. 📝 What to Write in Spec If You Can’t Lock Exact Yarn Count

If you don’t know the count, specify the outcome:

1. What is Density?

Density (Ends Per Inch / Picks Per Inch) is the number of threads in a square inch of fabric.

2. What Density Controls

• 🌬️ Wind Resistance: Higher density = warmer (less air passes through).
• 💪 Durability: Higher density = stronger structure.
• 🧵 Seam Slippage: Low density allows threads to pull apart at the seams.

3. EPI/PPI vs “Thread Count”

Don’t be fooled by high “Thread Counts” (like 1000TC) in marketing. In flannel, a balanced density (e.g., 64×54) is better than a super-high count which makes the fabric stiff and boardy.

4. Common Density Problems

5. Quick Ways to Check Density

Brushing (Napping) is a mechanical process that tears fibers to create fuzz. It is a “controlled damage.”

1. Single-Brushed vs Double-Brushed

• Single-Brushed: Brushed on one side (usually back).
• Double-Brushed: Brushed on both sides (Face & Back).

🔗 Read the detailed comparison

2. How Brushing Level Changes Performance

• Softness: Increases.
• Warmth: Increases (More loft).
• Pilling: Does brushing increase pilling risk? Yes, significantly.
• Strength: Decreases (Tear strength drops).

3. How Factories Describe Brushing

4. How to Verify Brushing Level

1. Only Looking at GSM

The Error: Ignoring density leads to weak fabrics. A heavy fabric with low density will fall apart.

2. Missing “Side” Definition

The Error: Ordering “Brushed” and getting the wrong side brushed. You must specify Face Side, Back Side, or Double Brushed.

3. No Shrinkage Method

The Error: Accepting “3% shrinkage” without knowing the method. 3% Line Dry is very different from 3% Tumble Dry (which might actually shrink 8%).

4. Subjective Terms

The Error: Using vague terms like “Super Soft” in the PO.

The Fix: Always reference a physical “Golden Sample Approval” for handfeel.

1. Incoming Quick Checks (⏱️ 30 Minutes)

• 📏 Width: Measure inside selvedge. Is it within tolerance?
• ⚖️ GSM: Cut 3 samples (Head, Middle, Tail). Weigh them.
• 🎨 Shading: Check Head vs Tail for color consistency.
• 🧸 Brushing: Compare handfeel to the Golden Sample.

2. Lab Checks (Before Approval) 🔬

• 🧺 Shrinkage: Wash 3 times (AATCC 135).
• ☁️ Pilling: Martindale or Random Tumble (ASTM D3512).
• 💧 Crocking: Rub dry and wet cloth (AATCC 8).

🔗 See full test list in Colorfastness Guide

3. Sampling Plan 📦

• 1️⃣ Lab Dip: Color approval.
• 2️⃣ Strike-Off: Print approval.
• 3️⃣ PPS (Pre-Production Sample): Wash test this sample!
• 4️⃣ Shipment Sample: Keep for records.

1. What does GSM mean for flannel fabric?

Flannel GSM stands for Grams per Square Meter. It indicates the weight and thickness.

• 130 GSM: Light (shirt)
• 170 GSM: Medium (bedding)
• 250 GSM: Heavy (jacket/blanket)

2. Is heavier flannel always warmer?

Not always. Does heavier flannel mean warmer? Usually, yes, but a lighter flannel with double brushing (high loft) can be warmer than a heavy, flat flannel because it traps more air.

3. What yarn count is best for flannel shirts?

What yarn count is best for flannel shirts?

• Standard casual shirt: 20s x 10s or 21s x 21s is ideal.
• Dressy, lightweight flannel: 40s x 40s is best.

4. Does higher density mean less pilling?

Generally, yes. Tighter weaves hold fibers in place better, reducing the loose fibers that form pills.

5. Single vs double brushed: which is better for bedding?

Single vs double brushed: For bedding, double brushed is standard because it provides maximum softness against the skin and maximum warmth.

6. How do I specify brushing level in a PO?

Use specific terms: “Light Nap,” “Medium Nap,” or “Heavy Nap.” Even better, attach a physical swatch and write “Brush to match sample handfeel.”

7. Why does flannel look lighter after washing?

Why does flannel look lighter after washing? Because the brushing process creates loose fibers (lint). The first wash removes this lint, slightly reducing the fabric’s weight.

8. What tolerances should I set for flannel specs?

What tolerances should be in a flannel spec sheet?

• GSM: ± 5%
• Width: -0 / +1 inch
• Shrinkage: Max 3-5% (depending on finish)

9. What’s the difference between peached and brushed?

Peached uses abrasive paper (sandpaper) to create a very short, velvet-like fuzz. Brushed uses wire bristles to pull out longer fibers, creating a fluffier, wool-like texture.

10. How do I prevent shade variation on flannel?

Nap direction & shading is critical. Ensure all rolls are brushed in the same direction and marked. Require a Shade Band approval before bulk shipment.