Understanding GSM and Paper Grades in Corrugated Manufacturing

GSM (Grams per Square Meter) measures paper weight and is the most important specification in corrugated manufacturing. Understanding GSM and paper grades helps you make better decisions about materials.

What is GSM?

GSM tells you how heavy paper is per square meter. Higher GSM = heavier, stronger paper.

Common GSM ranges in corrugated:

• 100-130 GSM: Fluting paper
• 140-180 GSM: Standard liners
• 180-250 GSM: Heavy-duty liners
• 250+ GSM: Specialty applications

Paper Types in Corrugated Boxes

1. Kraft Liner (Top Quality)

Made from: Virgin wood pulp (first use)

Characteristics:

• Brown natural color
• Highest strength
• Best print surface
• Most expensive

GSM options: 125, 150, 180, 200, 220, 250

Use for: Outer layer (visible side), export packaging, printing

2. Test Liner (Recycled)

Made from: Recycled corrugated and paper

Characteristics:

• Brown or mottled appearance
• Good strength (70-85% of kraft)
• Cost-effective
• Variable quality based on waste source

GSM options: 110, 140, 150, 170, 180, 200

Use for: Inner layer, secondary packaging, cost-sensitive applications

3. Semi-Chemical Fluting

Made from: Partially processed wood chips

Characteristics:

• Primary fluting material
• Good stiffness
• Consistent quality

GSM options: 100, 112, 120, 140, 150

Use for: Middle layer (flute)

4. Waste-Based Fluting

Made from: 100% recycled materials

Characteristics:

• Most economical
• Lower strength than semi-chemical
• Suitable for non-demanding applications

GSM options: 90, 100, 110, 120

Use for: Light-duty boxes, cost-priority applications

5. White Top Liner

Made from: Bleached kraft or coated paper

Characteristics:

• White or cream color
• Premium appearance
• Excellent print quality
• Higher cost

GSM options: 140, 170, 200, 230

Use for: Retail packaging, premium products, full-color printing

GSM Selection Guide

By Product Weight

By Application

E-commerce (light): 140 GSM kraft + 112 GSM flute E-commerce (medium): 150 GSM kraft + 120 GSM flute Industrial: 180 GSM kraft + 140 GSM flute Export: 200+ GSM kraft + 150 GSM flute Premium retail: 170 GSM white top + 120 GSM flute

Cost vs Performance Trade-offs

Increasing GSM by 30%:

• Material cost: +25-30%
• BCT improvement: +20-25%
• Stacking strength: +15-20%

Decision framework:

1. Calculate actual strength needed (BCT requirement)
2. Choose minimum GSM that meets requirement
3. Add safety margin (10-20%)
4. Consider customer expectations

Example: Customer needs BCT of 400 kg

• Option A: 3-ply with 180 GSM = 420 kg BCT, ₹18/box
• Option B: 3-ply with 150 GSM = 320 kg BCT, ₹14/box
• Option C: 5-ply with 140 GSM = 550 kg BCT, ₹22/box

Best choice: Option A meets requirement most cost-effectively.

Quality Indicators

Ring Crush Test (RCT): Measures paper's crush resistance

• Higher RCT = stronger boxes
• Typical: 6-10 kg/cm for good quality

Burst Factor: Resistance to rupture

• Important for filled boxes
• Typical: 15-25 for standard applications

Cobb Value: Water absorption

• Lower = more moisture resistant
• Critical for humid storage

Paper Quality by Source

Imported paper (Europe, North America):

• Consistent quality
• Higher cost (₹5-10/kg premium)
• Better for export packaging

Domestic Indian mills:

• Variable quality by mill
• Cost-effective
• Suitable for domestic use

Top Indian mills: JK Paper, ITC, Tamil Nadu Newsprint, Century Paper

Key Takeaways

1. Higher GSM = stronger but costlier - match to actual need
2. Kraft for outer, test liner for inner - optimize cost without sacrificing appearance
3. Semi-chemical fluting for strength, waste-based for economy
4. Test samples before bulk orders - quality varies by supplier
5. Consider total cost - including wastage, transport, and storage
6. Ask for certifications - RCT, burst factor, Cobb value