The Right Fiber Sizing is an Advantage No One Can Afford to Ignore.

Composites are quickly changing the way we drive, transport goods, generate energy, and more commonly, how industry handles problems that involve a maximum strength/minimal weight contradiction. The role sizing plays in the manufacture of composites is critical and complex. Our Hydrosize® family of products consists of sizing solutions that are specifically developed for use in the manufacturing of natural, carbon, and glass fibers, including chopped and continuous formats.

Sizing and Its Importance

“Sizing” is a thin, homogenous coating applied to the surface of fibers during the manufacturing process. Not only does it protect the fiber during its production, but also during post-processing operations such as handling, spreading, weaving, compounding, and moulding. Additionally, it helps in processing fiber into intermediary forms such as fabrics, braids, thermoset prepreg, and thermoplastic organo sheets.

Molten Glass Bushing Cooled Air Spray Water Spray MICHELMAN INVOLVEMENT Sizing Applied Contact Time <0.5ms To Secondary Processing at 20m/s Mix Sizing

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.

Pan Precursor Oxidation Carbonization Sizing MICHELMAN INVOLVEMENT Surface Treatment Carbon Fiber Spool Winding

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. There are 4 major effects of sizing variation on fiber production:

Effect of Sizing Variation on Fiber Production
Sizing Problem
Effect on Fiber

Particle Size

Changes 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:


Mechanical Properties

  • Impact resistance
  • Tensile strength
  • Flexural strength
  • Compressive strength
  • Fatigue resistance

Chemical Properties

  • Thermal & color stability
  • Hydrolytic stability
  • Corrosion resistance
  • Odor profile
  • Dispersion

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.

  • Integrity: Keeps the chopped bundles together
  • Chopping: Increases the chopper's blade life and reduces fuzz generation
  • Unwinding: Keeps the strand together
  • Weaving: Provides lubricity and flexibility to prevent breaks

The Interface

The sizing is the “glue” when sized fiber is introduced to the resin matrix. The forces between sizing and matrix can be chemical bonding, hydrogen bonding, and Van der Waals interaction. Michelman takes a chemistry-agnostic approach to solving interface adhesion problems, creating custom solutions that are optimized for the myriad combinations of polymers, the fibers & fillers to which they are applied, and the various manufacturing processes used to produce composites.

Engineering Resins High Temperature (PEEK, PPS) Olefin (PS, PE, PP) Polyester Polyurethane Vinyl Ester Glass Carbon Basalt Aramid UHMWPE Polymeric Natural Compounding Filament Winding Pultrusion Spray-up Hand Lay-up PROCESSES POLYMERS FIBERS & FILLERS
Product Name
Form Type
Product Solids Type
chopped strands
PA compatible
PC compatible
PE compatible
thermal stability
PET/PBT compatible
PP compatible
PPS/ETP compatible
thermosets compatible
adhesion promotion
block resistance
continuous fiber
impact resistance
slip and lubricity
chemical resistance
hydrolysis resistance
print receptivity
Hydrosize® HP-1632SolutionPolyimide
Hydrosize® HP3-02EmulsionPhenoxy Dispersion
Hydrosize® PA845DispersionPolyamide
Hydrosize® PA845HDispersionPolyamide
Hydrosize® PP2-01DispersionPolypropylene
Hydrosize® PP270EmulsionPolypropylene
Hydrosize® PP943EmulsionPolypropylene
Hydrosize® U1-03DispersionModified Polyurethane
Hydrosize® U2022DispersionPolyurethane
Hydrosize® U2023Specialty DispersionPolyurethane
Hydrosize® U5-02DispersionPolyurethane
Hydrosize® U6-01SolutionPolyurethane
Hydrosize® U7-01DispersionPolyurethane