Very Long Fiber (VLF) thermoplastics are injection moldable thermoplastic compounds that feature continuous fiber filaments running the full length of the pellet allowing these materials to exhibit simultaneous improvements in strength, stiffness, and impact resistance over a wide temperature range.

Heralded as an exciting growth area in thermoplastics, VLF composites are widely accepted as a viable alternative to traditional reinforced thermoplastics and metals for a vast array of applications.

RTP Company uses a pultrusion process to manufacture Very Long Fiber (VLF) thermoplastics, which entails pulling continuous fiber rovings through a polymer melt in a specialized processing die. The resulting composite strands are cooled and chopped into pellets.

Pultrusion is dramatically different than the process used to manufacture short glass fiber (SGF) thermoplastics where chopped fiber is melt-blended with plastic resin using conventional extrusion compounding methods. The fiber length in a SGF pellets is typically less than 1 mm while in VLF pellets, fiber length is up to 1/2 inch.

Wet-out refers to the impregnation of the fiber rovings with thermoplastic resin during the pultrusion manufacturing process. Successful wet-out completely coats the individual filaments and results in pellets that are free of loose fibers that can cause problems during conveying.

Standard pellet length for long fiber composites at RTP Company is 7/16 inch, or 11mm, although other lengths can be specified in the 6 to 12 mm range. Experience has shown that this length provides optimal properties while still allowing processing in standard injection molding equipment.

The fiber is the structural component of long fiber composites. The longer the fiber, the more effectively the polymer is able to “grab on” and transfer stress to the fiber. At lengths around 1/2 inch the strength of the fiber is fully attained, and longer lengths provide no significant improvement in physical properties while making the material more difficult to process.

Very Long Fiber (VLF) Compounds are available with glass, aramid, stainless steel, or carbon fiber reinforcement at loadings up to 60% by weight.

  • Glass fiber is the most popular and cost effective reinforcement used for VLF composites
  • Stainless steel fiber for its electrostatic dissipation (ESD) and electromagnetic interference (EMI) shielding properties
  • Carbon fiber provides additional enhancements in flexural modulus and potential weight reductions while also providing ESD properties

Available glass fiber loading levels for most thermoplastic resins are 20, 30, 40, 50, and 60% by weight. Balancing performance, cost, and weight are critical criteria in selecting a correct polymer to fiber ratio. In general, 40 and 50% loading levels are most common.

Polypropylene and Nylons are the most commonly utilized polymers for Very Long Fiber (VLF) compounds, but they can be produced in a number of other polymer systems including high temperature resin systems like PPS, PPA, and PEEK.

Our network of production facilities is located on the three continents (Asia, North America, and Europe) where major manufacturing enterprises are concentrated.

To ensure timely and efficient delivery our long fiber thermoplastic (LFT) composites are produced at three sites in North America (Winona, MN, Indianapolis, IN, and Monterrey, Mexico); at our European facilities in Beaune, France and Wroclaw, Poland; and at our facility in Suzhou, China. RTP Company is committed to adding additional manufacturing capacity as the market for LFT composites grows.


Very Long Fiber (VLF) composites bridge the price-to-performance gap between short glass fiber thermoplastic (SGF) materials and advanced composite materials while still being processable via efficient injection molding methods.

Successful end-uses often require greater performance than is attainable with SGF products and where metal is not a desirable option due to weight or per part costs. VLF Compounds have gained rapid acceptance as a viable alternative to die castings, metal assemblies, and traditional plastic materials in a vast array of markets, including: industrial equipment, automotive, consumer goods, sports and leisure, and information technology.

The benefits of Very Long Fiber (VLF) thermoplastic composites can be easily understood by examining the entangled long fiber matrix formed in a finished part. Exposing a molded part to pyrolysis conditions, commonly referred to as burn-off, removes the polymer and leaves behind the glass reinforcing fibers allowing visual examination. The fiber network that is formed by a VLF material retains the shape of the molded part and resembles a fiber perform with well and evenly distributed fibers.

The extensive fiber network in an VLF part improves many performance characteristics and also inhibits crack propagation. Often referred to as “stiff and tough”, VLF Compounds exhibit a wide range of performance advantages:

  • Better impact resistance and rigidity at elevated and sub-zero temperature ranges (up to 5 times that achieved with short glass fiber thermoplastics)
  • Modulus retention at elevated temperatures
  • Creep resistance under constant load in severe environments
  • Dimensional stability and resistance to warpage resulting from reduced shrinkage — which occurs as thermoplastic materials solidify during molding

Relative to short fiber materials, Very Long Fiber Compounds are slightly more expensive, but yield price-to-performance advantages that make them attractive for end-use applications that need an engineered material solution. Due to the efficiencies of the injection molding manufacturing process, VLF composites result in a lower per piece cost when replacing metal and provide a significant reduction in weight.

RTP Company has multiple engineers dedicated to long fiber composite product development. You can draw on their expertise during the application assessment and material selection process, or at anytime during your product development or manufacturing cycle. In total, RTP Company has over 70 R&D engineers with expertise across a variety of disciplines — ranging from color, conductive/antistatic, wear resistance, and flame retardants — who can assist with any application requirement you may have.

RTP Company has many specialty compounds certified to the automotive specifications of major OEMs. Please contact RTP Company to inquire about a specific standard to determine which materials are suitable.

Customizing materials to end-use requirements is a hallmark of RTP Company. Our experienced team of over 70 product development engineers are highly accessible and distributed worldwide, allowing them to answer your inquiries personally. Depending on usage volume, additional additives can be incorporated directly into our long fiber composites to meet your requirements or combined as a cube blended long-cut masterbatch.

Yes, RTP Company offers color masterbatches that can be combined with our long fiber products during molding; these masterbatches are optimized to preserve fiber length. Choose from our portfolio of standard colors or have our specialists custom match a color to your precise standard.

Application Development

Reasons for using Very Long Fiber (VLF) Compounds vary, but the most common reason is the increase of mechanical properties compared to Short Glass Fiber (SGF) Compounds – opening up the design window and allowing thermoplastic compounds to be used in more demanding applications.  Among the properties improved by VLF Compounds, the primary beneficiary is impact performance, with Izod impact values often more than doubling SGF Compounds.

Ask our engineers for a material recommendation! RTP Company has a streamlined application assessment process that considers many criteria, such as operating temperature, static or kinetic loads, impact, cost targets, and environmental considerations to identify a long fiber composite that will meet your applications’ demands. In-house design engineers can also be tapped ensure a smooth transition from concept through production.

Any of our product development engineers, regardless of their area of expertise, can help you identify your applications’ unique requirements and recommend a plastic compound that will meet your precise needs. Our engineers are polymer experts renowned for their accessibility and ability to solve your application problem.

Reinforced plastic compounds have replaced metal in many applications by providing better aesthetics, corrosion resistance, and opportunities for part consolidation. When choosing Very Long Fiber (VLF) composite materials, designers can now exploit these benefits when confronting demanding load requirements of structural components.

In instances where other reinforced plastics do not fulfill performance requirements of complex parts, VLF Compounds are the logical choice; designers regularly choose them to avoid typical metal concerns, such as corrosion, painting, and recycling. For example, die castings and metal assemblies are ideal applications for  the advantages of VLF Compounds.

Use of longer reinforcing fibers elevate the performance of thermoplastics to such a high degree that cheaper resins begin to provide the properties of more expensive engineering polymers. In many instances, VLF Compounds have proven themselves to be an economically viable alternative to other reinforced plastics. Contact any of our sales engineers for assistance in examining the differences between available reinforcing technologies.

RTP Company’s global Technical Service team is available to provide expertise regarding design analysis, mold construction, pre-production trials and trouble-shooting. A wide variety of Computer Aided Design analysis and metal replacement tutorial services are also available.

Many die cast tools can easily be modified to allow them to be used for plastic injection molding. Often, this is a convenient first step in creating a meaningful prototype to measure success potential for changing materials.

Samples of our long fiber composites, or any other RTP Company product, can be obtained by contacting a sales engineer or business manager who servers your geographic area or market segment. To locate an RTP Company representative, visit Find Your Representative, or call us at 1-507-454-6900.

Processing & Handling

Typically, specialty compounds manufactured by RTP Company, including VLF Compounds, are packaged in 1,100 pound gaylord bulk material boxes. When ordered in 40,000 pound quantities VLF materials can be delivered via bulk truck and directly conveyed into your material silo.

Yes, care should be taken to maximize fiber length in the molded article to maintain physical properties. Typical accommodations include: use of free flowing check-rings and general purpose screws; generous mold gates and runners; and radiused corners and direction changes.

All reinforced plastics, particularly those with fiber ends, are more abrasive to molding machinery than unfilled resins. Since long fiber composites have fewer fiber ends than an equal loading by weight of short fiber material, it wears less on equipment.

No special equipment is required to injection mold Very Long Fiber (VLF) composites. However, to produce quali