Breather Fabric
VAC Innovation’s breather fabric (also called breather cloth) is a 100% non-woven polyester (or nylon) felt used in composite vacuum bagging. Under vacuum it provides a continuous “breather” path so that air and volatiles can escape and resin can bleed away from the laminate. In practice, a thin layer of breather is placed between the peel ply and the vacuum bag. Its needle-punched fibre construction gives it a high loft and porosity, allowing uniform air evacuation and pressure distribution over complex part shapes. In short, breather fabric ensures a complete vacuum path and even compaction; it can also absorb excess resin if a perforated release film is used.
Breather cloth thus helps prevent voids and dry spots during cure. When a non-porous release film is used, the breather simply maintains the vacuum path without soaking resin. If a perforated (hole-punched) release film is used, resin will bleed through into the breather layer, allowing controlled resin bleed-out and easier clean-up. In either case, breather fabric can be left in place during cure; if it acts as a bleeder then it’s removed and discarded afterward.
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Needle-Punched Non-Woven vs Woven
Our breather fabric is a needle-punched polyester felt, i.e. a non-woven material formed by mechanically bonding fibres. This contrasts with any hypothetical woven breather. In fact, industry suppliers emphasize that non-woven breather is safer and more effective than woven fiberglass alternatives. Non-woven breather has superior drapability (it easily conforms to corners and curves) and no warp/weft structure to tear or shed strands. It also tends to have higher porosity for airflow. In short, our needle-punched polyester/nylon breather offers excellent stretch, conformability and airflow – ideal for vacuum bag moulds – with none of the handling issues of a rigid woven cloth.
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VAC Innovation Breather Products
VAC Innovation offers three breather fabric variants, all needle-punched (non-woven) and white in colour, rated to 200 °C for high-temperature cures. Their specifications are:
• VACB4 (Lightweight Breather)
150 g/m² (4.4 oz/yd²), 2.5 mm thick (uncompressed). This light, highly drapable breather is ideal for complex shapes and conforms easily to tool contours.
• VACB10 (Heavyweight Breather)
340 g/m² (10 oz/yd²), 4 mm thick. The heavier fibre content makes it suited for large flat panels or high-pressure/autoclave use (up to 200 °C) while still providing good drape.
• VACBN10 (High-Flow Breather) –
335 g/m² (10 oz/yd²), 4.2 mm thick, 80% nylon/20% polyester. This heavyweight variant has similar thickness and temperature rating (200 °C) to VACB10 but with higher airflow thanks to the nylon blend – useful when maximum gas escape is needed.
Each breather roll is 60 in (1.5 m) wide (also available in narrower slit widths). In use, these needled fabrics act as a breather/absorption medium (per the VAC Innovation catalogue): under vacuum they let air pull evenly through the entire layup while channelling excess resin into the voids if allowed. Importantly, these needle-punched breathers conform to the part and do not impart texture (unlike peel ply), and they are binder-free, so they do not outgas or contaminate the laminate. Compared to woven alternatives, our needled breather is drapier and forms a “blanket” of fibres that supports even vacuum pressure across the part.
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Applications & Best Practices
In practice, breather fabric is used in all standard vacuum bagging processes. It is especially recommended for wet lay-up and prepreg cures under ~40 PSI (full vacuum) up to ~200 °C. Key uses and tips include:
• Air & Gas Evacuation:
Always include breather cloth between the release ply and the bag’s vacuum port. It provides a path for trapped air/vapor to flow to the pump. This avoids air pockets and helps the entire laminate compress uniformly under vacuum.
• Even Pressure:
The breather’s fibre network distributes vacuum pressure evenly. Complex parts (curves, corners) benefit because the non-woven felt moulds into shape.
• Resin Bleeding (optional):
If the goal is to remove resin (as with bleeder fabric), use perforated release film. The resin will wick into the breather layer, leaving a cleaner laminate. If you want to keep resin in the part, use a non-porous release film and the breather will simply maintain the vacuum path without soaking up resin.
• Reusability:
Non-porous (solid) release films allow the breather to be reused on future layups since it won’t be contaminated by resin. Porous films will foul the breather with resin, so typically it is discarded after a resin-bleed cure.
• Temperature & Pressure:
Our breather fabrics are rated to 200 °C (392 °F), making them suitable for most epoxy/autoclave cures. Note that special fiberglass or high-temp breathers exist for >400 °F, but our polyester breather is ideal for standard autoclave and oven processes.
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Key Benefits of Needle-Punched Breather Cloth
• Continuous Vacuum Path:
Ensures all areas of the bag are evacuated.
• Conformability:
Folds and pleats naturally to part contours (corners, curves) without bridging. The air channels remain open under vacuum.
• Resin Management:
Acts as an absorption layer when combined with perforated release, capturing excess resin and yielding a cleaner finish.
• Temperature Resilience:
Withstands high cure temps (up to 200 °C) without shrinkage or outgassing.
• Simplicity:
No special handling (no need to stretch or fix – just cut and lay in). Compared to woven alternatives, there’s no risk of fibre protrusion or dust, making it safer and cleaner in the shop.
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