Before PTFE coating, resin impregnation, or lamination, fiberglass fabric must be pre-dried. The purpose may be simply removing moisture, or it may involve burning off textile sizing agents (dewaxing), or warming the fabric to a stable temperature before coating. Each purpose requires different temperature and time settings.
Incorrect parameters can lead to poor impregnation, weak bonding, fabric yellowing, loss of strength – or even complete scrap.
Aokai PTFE has extensive experience in glass fiber processing. This guide explains the three main treatment categories, their optimal temperature ranges, time control, and practical tips for consistent results.
Three Main Treatment Purposes and Their Temperature Ranges
Treatment Purpose
Temperature Range
Core Objective
Typical Applications
Moisture removal (most common)
105°C – 120°C
Remove adsorbed water without damaging sizing agents
Lamination, PTFE/silicone coating, prepreg layup
Dewaxing / thermal cleaning (sizing removal)
300°C – 450°C
Completely burn off textile sizing (starch, PVA, etc.)
Processes requiring ultra-clean surface: resin impregnation, chemical treatment
Preheating for process transition
60°C – 100°C
Raise fabric temperature for coating or impregnation
Continuous coating lines, before glue dip tanks; prevents resin viscosity rise from cold fabric
Routine Moisture Removal – The Most Common Process
This is the standard pre-drying step for most fabric before coating or lamination. The goal is thorough dehumidification while protecting the sizing agents that hold the fibers together.
1. Temperature control
For general electronic and reinforcing fabrics: maintain 105°C – 120°C.
For fabrics treated with silane coupling agents: keep temperature below 110°C to avoid breaking the coupling bonds.
The temperature deviation inside the oven must be controlled within ±5°C to prevent local overheating.
2. Time control (based on fabric weight)
Fabric Weight
Recommended Time
Thin fabric (<100 g/m²)
10 – 15 minutes
Medium & heavy fabric (200 – 400 g/m²)
20 – 30 minutes
Thick fabric / mat (>600 g/m²)
1 – 2 hours or longer
Termination criterion: Constant weight is achieved when the weight difference between two consecutive measurements is less than 0.1%. For rolled fabrics, hang them loosely or use spacer strips during drying to avoid the problem of dry exterior but damp interior.
3. Key control points
The oven must have forced dehumidification. Open fresh air valves to discharge humid air timely.
Do not overload the oven; ensure airflow around each roll or sheet.
Dewaxing and Thermal Cleaning – For Ultra-Clean Surfaces
When the fabric must be completely free of organic sizing agents (e.g., before high-performance resin impregnation for aerospace or high-temperature composites), thermal cleaning is required.
1. Temperature control
Volatilization & smoking stage: around 300°C. Requires sufficient oxygen and effective smoke exhaust.
Residue burnout stage: gradually raise temperature to 380°C – 450°C and hold, to fully oxidize residual carbon.
Never exceed 500°C – otherwise the fiberglass itself will become brittle and damaged.
2. Time control
For continuous thermal desizing furnaces, adjust fabric running speed to ensure the fabric stays in the high-temperature zone for several to more than ten minutes, depending on fabric weight. Heavier fabrics need longer exposure.
3. Acceptance criteria
Loss on ignition (LOI) shall be less than 0.1%. This is the gold standard.
Simple field test: Ignite a fabric corner with a lighter. Qualified material produces no black smoke or peculiar odor, with minimal ash residue.
Qualified fabric appears white or retains its original color, without black spots or yellow streaks.
4. Follow-up notes
Dewaxed fiberglass fabric has high surface activity. Transfer it to the next impregnation process immediately, or seal and package properly to prevent re-absorption of moisture and contamination.
Preheating Before Coating – For Process Stability
Before applying PTFE emulsion or silicone rubber coating, the fabric may need gentle preheating to a stable temperature.
1. Preheating parameters
Set temperature: 60°C – 80°C, slightly above the ambient dew point to avoid overly fast surface drying of coatings.
Residence time: usually dozens of seconds to one or two minutes via short-range infrared or hot air ovens – just enough to bring the fabric to the target temperature.
2. Practical operation guidelines
Take actual fabric temperature as the standard, not oven air temperature. Use infrared thermometers or accompanying temperature measuring devices for real-time monitoring.
Uniform air flow & circulation – hot air convection determines drying efficiency. Uniform wind speed ensures even temperature distribution across the fabric width.
Preliminary sample test: Different batches may use different sizing agents. Take small samples and dry them at different temperatures (105°C, 120°C, 130°C, etc.). Observe surface discoloration and strength changes to confirm the maximum safe temperature for each batch.
Storage After Drying – Prevent Re-Contamination
Dried fabric, especially dewaxed fabric, is hygroscopic and easily contaminated.
If not for immediate use, seal in aluminum foil bags with desiccants.
Alternative: store in a drying room with temperature below 30°C and relative humidity under 40%.
Recommended usage window: within 4 to 8 hours after drying for best results. Beyond that, re-dry before use.
Aokai PTFE tip: For high-reliability applications (aerospace composites, high-voltage insulation), we recommend using the fabric immediately after drying or within 2 hours.
Aokai PTFE provides pre-drying specifications for all our fiberglass fabrics. For critical applications, we can supply fabric that is pre-dried and vacuum-sealed ready for immediate use. Contact us for custom drying parameters based on your fabric type and subsequent process.
If you wish to know more about detailed specifications, application scenarios and customized solutions for our full product range, including PTFE high-temperature fabrics, PTFE high-temperature tapes, PTFE mesh belts, seamless bonding machine belts, single-sided PTFE cloth, high-temperature resistant conveyor belts and high-temperature resistant fiberglass fabrics, please contact us:
