FILCO® 661 S is a bisphenolic, unsaturated polyester resin available in powder form. Characterized by its very high molecular weight, rapid solubility in styrene, and notable binding power for glass fibers, especially in "hot melt" conditions, this resin demonstrates a high degree of compatibility with unsaturated polyester matrices. It surpasses type 661 with a higher flow rate, ensuring improved processing capabilities. Notably, FILCO 661 S exhibits excellent dispersability in water and offers heightened resistance to agglomeration compared to type 661, establishing it as a versatile and efficient component for composite manufacturing processes.

Functions: Resins, Binders & Matrix Materials

Chemical Family: Bisphenols, Polyesters, Unsaturated Polyester (UPE)

Compatible Polymers & Resins: Unsaturated Polyester (UPE)

Technical Data Sheet

Ask P.A.T. Products Questions

Leo Coyle avatarErik Espling avatarLogan York avatar

Enhanced TDS

Identification & Functionality

Composite Materials Functions

Features & Benefits

Product Highlights

FILCO 661 S is a bisphenolic, unsaturated polyester resin in powder form

  • Very high molecular weight
  • Very quickly soluble in styrene
  • High binding power for glass fibers in "hot melt" operating conditions
  • High degree of compatibility with unsaturated polyester matrices
  • Higher flow rate than type 661
  • Very good dispersability in water
  • Higher resistance to agglomerate than type 661.

Applications & Uses

Compatible Polymers & Resins
Compatible Reinforcements

FILCO® 661 S main application

  • Styrene soluble binder for chopped strand mat and continous filament mat
  • Binder for preforms.
Processing Information

2,5 - 5% of FILCO® 661 S on the glass weight is normally required according to the weight for square meter and stiffness wanted for glass mat. Water as fine mist is sprayed to help FILCO 661 S to stick to glass fibers. After application of FILCO® 661 S the glass mat is stoved at 180 - 210 °C for 1 - 2 minutes. The operation lets water evaporate and melt FILCO® 661 S, which accumulates at the contact points of the glass strands, binding them.


Physical Form
Light yellow, free flowing powder
Typical Properties
ValueUnitsTest Method / Conditions
Acid Number12 - 18mg KOH/gMA018LCP
Melt Index (at 125°C)15 - 25g/10 minutesMA109RPL

Packaging & Availability

Packaging Type
Regional Availability
  • Canada
  • Mexico
  • USA
Packaging Information

FILCO® 661 S is supplied in fiber drums with polyethylene bag, net weight 120 kg

Storage & Handling

Shelf Life
12 months
Storage and Shelf Life Conditions

FILCO® 661 S should be stored in closed containers away from direct sun rays and source of heat, at temperature below 30°C. In these conditions, maximum suggested storage time is 12 months from production, in the original package. After that date the product must be rechecked.