Composite manufacturing depends on materials that most people never see and rarely think about, and the release liner is one of the most important of them. Every layer of resin-infused fabric, every roll of prepreg, and every vacuum-bagged layup relies on a release liner to contain resin, protect surfaces, and separate cleanly at exactly the right moment in the process. Issues like resin bleed, surface defects, dimensional shifts, or a prepreg roll that will not process correctly on the line can be the result of not specifying the appropriate release liner. Fox River Associates has spent more than 35 years supplying release liner solutions to North American converters and composite manufacturers, and because release liner is the only business we are in, our team brings a level of focused expertise to composite applications that a generalist supplier cannot match.
Specifying a release liner for a new or existing composite application? Call Fox River Associates today at 1-800-647-6579 or complete the form on this page. Our release liner specialists are ready to help you identify the right solution.
Why Siliconized Release Liners Are Essential in Composite Manufacturing
- A siliconized release liner performs several jobs at once in a composite process, and each matter to the quality of the finished part.
- The release liner supports resin during layup and cure, preventing bleed-through and keeping resin exactly where it belongs.
- The release liner protects the composite surface from contamination during handling, storage, and transport.
The release liner allows fabricators to handle tacky, resin-coated materials without them sticking to tooling, rollers, or each other, thanks to the non-stick surface the silicone coating provides.
The release liner may also contribute to surface finish, since the texture and characteristics of the release liner itself can influence the final surface of the cured composite part.
Because composite processes involve heat, pressure, vacuum, and sometimes aggressive resin chemistries, a release liner used in this industry has to hold up to demands that few other release liner applications require, which is exactly why composite manufacturers rely on Fox River Associates to benefit from their genuine technical depth in release liner selection.
Prepreg: The Most Common and Critical Composite Application
Of all the applications a release liner serves in composites, prepreg manufacturing is both the most common and the most demanding. Prepreg, short for pre-impregnated fiber material, consists of fiber reinforcement, whether unidirectional (UD) tape, woven fabric, or tow, pre-coated with a partially cured resin system. During manufacturing, the release liner acts as the carrier and protective barrier for that resin-coated fiber as it is produced, wound, stored, and later unwound for layup.
Two prepreg formats place particularly specific demands on release liner performance: (1) unidirectional and fabric prepreg, produced on wide web lines where the release liner must maintain uniform release and dimensional stability across the full width, and (2) drum-wound or tape-wound prepreg, where the release liner is spooled under tension alongside narrow tape and must release cleanly and consistently through every layer of the roll.
The release liner used in prepreg manufacturing must also match the resin cure chemistry. Hot melt prepreg processes apply resin at elevated temperatures, so the release liner must withstand sustained high heat without degrading, distorting, or transferring residue into the resin. Solvated prepreg processes, by contrast, expose the release liner to solvents during resin impregnation, which means chemical resistance and dimensional stability under solvent exposure become the priority. In both cases, dimensional stability is critical: a release liner that expands, shrinks, or wrinkles as it moves through a prepreg line will telegraph those defects directly into the resin-coated material riding on top of it.
Fox River Associates supplies release liner products engineered specifically for these demanding composite industry conditions. Our paper release liners are produced under controlled conditions with thermally cured silicone coatings and carefully managed moisture content. Because paper naturally absorbs and releases moisture with humidity, and the curing process itself removes moisture that must be properly reintroduced to keep the release liner dimensionally stable in the field, moisture content in paper release liners is a critical performance characteristic.
Getting composite specifications for release liners right the first time saves prepreg producers from costly line disruptions and material waste, and it is exactly the kind of application where a call to Fox River Associates at 1-800-647-6579 or a submission through the form on this page can save significant time and expense.
Beyond Prepreg: Other Composite Applications for Release Liner
While prepreg manufacturing is the leading application, release liner plays an equally significant role throughout the broader composite manufacturing process. In vacuum bagging, release liner materials function as a barrier between the layup and the vacuum bag or breather materials, allowing air to be evacuated and resin flow to be managed without the part sticking to surrounding materials during cure. In debulking, the intermediate compaction step used to remove trapped air and consolidate multiple plies, release liner facilitates clean separation between layers without disturbing the layup underneath. In composite panel production, whether for aerospace interior panels, structural automotive components, or industrial products, release liner protects resin-infused fabric layers as they are stacked, pressed, and cured. These processes span a wide range of end markets:
- In aerospace, release liner is used to produce airplane wings, interior panels, flooring systems, and luggage compartments.
- In sporting goods, it supports the manufacturing of items such as pickleball paddles, skateboards, golf shafts, bicycle frames, and hockey sticks.
- In automotive, release liner is used in body panels, hoods, and structural reinforcements.
- In broader industrial applications, it supports pressure vessels, pipes, wind turbine blades, and composite tooling boards.
Across every one of these markets, the release liner specification must match the resin system, cure method, and dimensional tolerance of the part being produced, and that is precisely the kind of cross-application knowledge Fox River Associates brings to every customer conversation.
Paper Release Liner or Film Release Liner: How to Choose for Composite Applications
One of the questions composite manufacturers ask is whether to specify a paper release liner or a film release liner, and the honest answer is that it depends on the process, the resin system, and the performance priorities of the application. A paper release liner, built on substrates such as glassine, supercalendered kraft (SCK), or clay-coated kraft (CCK), is often the right choice when cost efficiency, sustainability, and reliable performance in standard prepreg and composite panel processes are the priority. Paper release liner substrates perform well in many prepreg and layup applications and are often specified for lower-cost or less demanding production runs where a film release liner's added performance isn't required.
A film release liner, built on substrates such as PET, polypropylene (PP), or polyethylene (PE) in flat or embossed constructions, is generally the better choice when the application calls for superior dimensional stability, chemical and solvent resistance, high-heat tolerance, or the clarity needed for precise visual inspection of the layup underneath. Film release liner products are commonly specified for hot melt prepreg processes, solvent-exposed layups, and applications where any dimensional shift in the release liner could translate directly into a part defect.
Fox River Associates carries a full breadth of both paper release liner and film release liner products, along with specialty substrates for unusual requirements. Our team is uniquely qualified to collaborate with you to recommend the substrate that fits your process and resin system.
Non-Silicone Release Liner Options for Composites
Specialized composite and adhesive bonding processes are sensitive to silicone contamination, particularly in aerospace secondary bonding, painting, and surface preparation steps, where even trace silicone transfer from a release liner can interfere with adhesion or downstream coating performance. For these applications, Fox River Associates supplies non-silicone release liner options, including specialty-coated PET film release liner products engineered to deliver reliable, controlled release without introducing silicone into the process. Identifying when a silicone-free release liner is required, rather than a standard silicone-coated product, is exactly the kind of technical judgment call our team helps customers make, so the release liner supports the application instead of creating a downstream contamination risk.
What Fox River Associates Brings to Every Composite Application
Selecting the right release liner for a composite application depends on three things coming together, and this is where Fox River Associates has built its business over more than three decades:
- Breadth of product offering. Our release liner portfolio spans film, paper, and specialty substrates, giving composite manufacturers access to the full range of options needed to match resin chemistry, cure method, and part tolerance, regardless of your market application or your adhesive and chemical compound.
- Deep knowledge of composites and manufacturing processes. Because release liner is our sole focus, our team maintains a level of technical understanding of how resin systems, silicone and non-silicone coatings, and converting processes interact that a generalist supplier simply does not maintain, and we use that knowledge to identify the applicable release liner options for every specialized composite application.
- Service programs built around what converters and composite manufacturers need. Fox River Associates carries ample stocked inventory across our core release liner product lines, so customers never risk a production disruption because material was not on hand. For new and emerging composite applications, and for small to medium-sized converters who cannot commit to large minimum order quantities, we offer small minimum order quantities that make it practical to qualify and launch new applications without excess inventory risk.
We back this with what we believe are the industry's shortest lead times. And our ISO 9001:2015 certification reflects a formally audited quality management system governing how we source, handle, and ship release liner products, giving composite manufacturers a documented, repeatable process behind every roll they receive, which matters enormously in industries like aerospace where traceability and consistency are non-negotiable.
Talk to a Composite Release Liner Specialist
Whether you are specifying a release liner for a new prepreg line, troubleshooting resin bleed or dimensional issues in an existing composite process, or evaluating whether a paper release liner, film release liner, or non-silicone release liner is the right fit for your application, Fox River Associates is ready to help. Our team combines more than 35 years of release liner experience, ISO 9001:2015-certified quality processes, and inventory built to keep your production running, with the sole purpose of helping North American composite manufacturers and converters get their release liner specification right.
Call us today at 1-800-647-6579 or fill out the form on this page, and a member of our team will follow up promptly to discuss your composite release liner needs.