Understanding Fabric Air Permeability and Its Impact on Paper Quality

Air Permeability: A Critical PMC Specification

Air permeability, measured in CFM (Cubic Feet per Minute) or m³/m²/h, is the most important specification for forming fabrics and dryer fabrics. It directly impacts dewatering, drying rate, and paper quality.

What Is Air Permeability?

Air permeability measures how easily air flows through a fabric under a given pressure differential. In papermaking:

• Higher CFM = Faster dewatering (forming) or vapor transport (drying)
• Lower CFM = Slower but potentially more uniform results

Forming Fabric CFM Guidelines

Paper Grade	Recommended CFM	Notes
Tissue (14–22 gsm)	500–600	High dewatering for low basis weight sheets
Fine Paper (60–120 gsm)	400–500	Balanced dewatering and formation
Packaging (80–200 gsm)	350–450	Controlled dewatering for heavier sheets
Kraft (90–150 gsm)	300–400	Lower CFM for high-consistency stock

Dryer Fabric CFM Guidelines

Dryer Section	Recommended CFM	Reason
First Dryer Group	600–750	Maximum evaporation rate
Middle Dryer Groups	500–650	Controlled drying
Final Dryer Groups	400–500	Sheet conditioning

Air Permeability Testing

Regular permeability testing helps identify:

1. Fabric contamination requiring cleaning
2. Uneven wear patterns
3. Performance degradation before visible damage occurs

Track CFM values monthly to optimize replacement timing.