Reinforced Plastic Composites

Fiber Sizing

What is a Fiber Sizing?

"Sizing" is a thin, homogenous coating applied to the surface of fibers during the manufacturing process to protect the filaments during handling, and processing, and also during subsequent compounding and composite processing.  On the fiber surface, the sizing plays an important role in determining the properties of the final composite, such as improved adhesion between the fiber and the matrix, mechanical properties, chemical or water resistance, and thermal stability.

Michelman has developed families of film formers, binders, and lubricants formulated specifically for the fiber manufacturing process that address the unique challenges the industry faces. We have solutions for fiberglass, carbon fiber, natural fiber, and specialty fibers in chopped or continuous form.

Sizing Formulation

Fiber producers create their own, unique sizing formulations to deliver the best performance attributes to the fiber. These formulations are composed of water, silane coupling agents (specifically for glass and basalt fiber), film formers in dissolved, emulsified, or dispersed form, and a range of additives or modifiers such as surfactants, plasticizers, anti-static agents, antifoams, and rheology modifiers. These ingredients are carefully mixed together and delivered to the fiber to perfectly match the requirements of the targeted applications. Michelman has developed a range of lubricants, binders, and film formers exclusively formulated for the fiber manufacturing process that deal with the unique challenges faced by the industry.

The Film Former

When it comes to the manufacturing and further processing of fiber, the film former plays an important role in both the fiber's physical characteristics and finished composite properties. It provides improved adhesion and facilitates effective load transfer between the fiber and the matrix polymer, while imparting mechanical properties such as tensile strength, fatigue resistance, and impact resistance. Hundreds of film former dispersions are commercially available, but only a small percentage of them are compatible with other sizing ingredients. Michelman's technology allows customers to tailor the surface chemistry of reinforcement fibers to the chemistry of the matrix resin, thereby optimizing the interfacial adhesion between the polymers and fibers.

Sizing Stability

Stability is one of the key characteristics that fiber manufacturers take into consideration when selecting raw materials for their sizing formulations. View the graph to the right to see the four major effects of sizing variation on fiber production:

Sizing ProblemEffect on Fiber
Particle sizeChanges in Loss on Ignition (LOI)
Short shelf-lifeIncrease in manufacturing downtime
PH changesGain or loss of sizing pick-up on fiber
FoamFuzz, changes in LOI, uneven coverage

Sizing Benefits

Sizing benefits composite performance by optimizing the fiber-polymer interfacial adhesion. Not only does it protect the freshly formed fiber surface from abrasion, prevent fiber breakage at contact points, and preserve chopped bundles of fiber; sizing enhances the performance of a number of mechanical and chemical properties.

Processing Benefits

Sizing optimizes the processability of fiber. Although sizing is a small percentage of fiber reinforced composites–normally 0.5 - 5% of its weight–it affects the production and the processing of the fiber, and has a significant impact on the interface properties between the fiber surface and the composite matrix.



Hydrosize® film forming dispersions optimize the surface chemistry of reinforcement fibers that are integral to high performance composites. The diverse Hydrosize product range is optimized for a broad range of thermoplastic, thermoset, and very high temperature resin matrices. Hydrosize is applied during the manufacturing process of chopped or continuous strand fiberglass, carbon fiber, and natural fibers and fillers.

Product Name
Form Type
Percent Non-Volatile
Emulsifier Charge
FGLASS™ X90Solution39–41N/A
Hydrolube® 480Emulsion39.5–40.5Nonionic
Hydrolube® 496Emulsion28–31Nonionic
Hydrolube® 723Emulsion31.5–32.5Nonionic
Hydrolube® 743Emulsion31.5–32.5Nonionic
Hydrolube® 763Dispersion9.5–10.5N/A
Hydrosize® Carbon 110Dispersion34–36Anionic / Nonionic
Hydrosize® Carbon 120Emulsion34–36Anionic / Nonionic
Hydrosize® Carbon 210Dispersion58–60Anionic / Nonionic
Hydrosize® Carbon 220Dispersion58–60Anionic / Nonionic
Hydrosize® Carbon 240Specialty Dispersion58–60Anionic / Nonionic
Hydrosize® Carbon 250Dispersion55–58Anionic / Nonionic
Hydrosize® Carbon 260Solution28–32Anionic / Nonionic
Hydrosize® Carbon 280Dispersion28–32Anionic
Hydrosize® Carbon 310Emulsion30–33Anionic / Nonionic
Hydrosize® Carbon 410Solution10–12
Hydrosize® HP-1632Solution10–12N/A
Hydrosize® HP3-02Emulsion30–33Anionic / Nonionic
Hydrosize® PA845Dispersion22–24Anionic
Hydrosize® PA845HDispersion28–32Anionic
Hydrosize® PP2-01Dispersion38.5–41Anionic / Nonionic
Hydrosize® PP270Emulsion34.5–35.5Anionic / Nonionic
Hydrosize® PP943Emulsion39.5–40.5Anionic / Nonionic
Hydrosize® U1-03Dispersion49–52Anionic / Nonionic
Hydrosize® U2022Dispersion58–60Anionic / Nonionic
Hydrosize® U2023Specialty Dispersion59–61Anionic / Nonionic
Hydrosize® U5-02Dispersion54–56Anionic / Nonionic
Hydrosize® U6-01Solution28–32Anionic / Nonionic
Hydrosize® U7-01Dispersion55–59Anionic / Nonionic
Michem® Emulsion 42035AEmulsion34.5–35.5Cationic/ Nonionic
Michem® Emulsion 43240Emulsion39.5–40.5Anionic / Nonionic
Michem® Emulsion 48625M1Solution23.5–26N/A
Michem® Emulsion 91735Emulsion34–36Anionic / Nonionic
Michem® Emulsion 93135MEmulsion34.5–35.5Nonionic
Michem® Lube 743PEmulsion31.5–32.5Nonionic