What is FSI and Why Is It Important?

FAQ

FSI (Fiber Support Index) quantifies the number of support points per unit area on the paper-side surface of forming fabrics.

Each MD/CD yarn intersection creates a fiber anchoring point. Higher FSI = more uniform fiber mat = better retention + fewer sheet defects.

Typical FSI Ranges by Structure:

• Single Layer: 50-80
• Double Layer: 80-120
• Triple Layer: 130-170
• SSB: 150-200+

Recommendation: Culture paper and tissue grades should target FSI >150 for minimal sheet marking and best formation quality.

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Technical Background

This answer is based on PAPTEX's expertise in Forming Fabric. PAPTEX provides engineered fabric solutions to 200+ paper mills worldwide.

Related Resources

• 📖 View our Product Knowledge for more information
• 📋 Browse Forming Fabric related articles
• 📞 Contact PAPTEX Engineers for personalized recommendations for your paper machine

Last updated: July 2026