Cabosil Cabot M-5 Fumed Silica – 10 lb Bag

CAB-O-SIL M-5 Fumed Silica – 10 lb Bag

CAB-O-SIL® M-5 Fumed Silica, commonly referred to as Cabosil, is a lightweight, high-purity silica powder used to thicken resin systems and create controlled, non-sag mixtures for fiberglass, marine and composite applications.

The 10 lb CAB-O-SIL bag is ideal for professional boatbuilders, fiberglass repair shops, composite manufacturers, marine facilities and other high-volume users that regularly make bonding compounds, fillets, putties and thickened resin mixtures.

What Is Cabosil Used For?

Liquid resin is designed to flow and wet out fiberglass reinforcement. For bonding, filleting, gap filling and vertical applications, however, that same flow can make the resin difficult to control. Adding Cabosil / CAB-O-SIL fumed silica increases the viscosity of the resin and allows the user to create a thicker, more workable mixture.

Depending on how much CAB-O-SIL is added, a resin mixture can range from slightly thickened to a heavy, non-sag paste.

Common CAB-O-SIL Applications

• Fiberglass repair
• Boatbuilding and marine repair
• Composite fabrication
• Structural bonding mixtures
• Epoxy fillets
• Gap filling
• Vertical and overhead repairs
• Thickening polyester resin
• Thickening vinyl ester resin
• Thickening epoxy resin
• Creating non-sag adhesives and putties
• Helping prevent fillers and pigments from settling

Using CAB-O-SIL With Resin

There is no single universal mixing ratio for Cabosil. The amount required depends on the resin system, temperature and desired consistency.

Always add CAB-O-SIL gradually while mixing until the desired viscosity is reached. Because fumed silica is extremely lightweight, a relatively small amount can significantly change the consistency of the resin.

Typical Consistencies

• Lightly Thickened: Reduces resin flow while remaining easy to spread.
• Mayonnaise Consistency: Common for bonding, bedding and adhesive applications.
• Peanut Butter Consistency: Useful for fillets, gap filling and applications requiring strong sag resistance.

CAB-O-SIL With Epoxy Resin

When thickening a two-part epoxy system, first measure and mix the resin and hardener according to the epoxy manufacturer's specified ratio. After the resin and hardener are thoroughly combined, gradually blend in CAB-O-SIL until the desired consistency is achieved.

This makes Cabosil especially useful for creating epoxy bonding adhesives, filleting compounds and non-sag repair mixtures.

CAB-O-SIL With Polyester and Vinyl Ester Resin

CAB-O-SIL can also be used to control the viscosity of many polyester and vinyl ester resin systems. Gradually blend the fumed silica into the resin before completing the catalyzed mixture, following the resin manufacturer's specific catalyst and processing instructions.

CAB-O-SIL vs. Q-Cell

CAB-O-SIL and Q-Cell serve different purposes.

CAB-O-SIL is primarily used when you need:

• Resin thickening
• Sag resistance
• Structural bonding consistency
• Filleting
• Gap filling

Q-Cell and similar lightweight fillers are generally better suited for fairing applications where easy sanding is important.

CAB-O-SIL creates a harder cured mixture and is not primarily designed as an easy-sanding fairing filler. In some applications, Cabosil and lightweight fillers may be used together to balance sag resistance, bulk and sandability.

Why Buy CAB-O-SIL in a 10 lb Bag?

Fumed silica has an extremely low bulk density, meaning 10 pounds of Cabosil represents a substantial volume of material. The 10 lb bulk bag is an excellent option for shops and manufacturers that regularly use resin thickening additives and want to reduce the cost of repeatedly purchasing smaller containers.

Recommended for:

• Boat manufacturers
• Boatyards
• Fiberglass repair shops
• Composite manufacturers
• Marine service facilities
• Tooling and mold shops
• Professional epoxy users

Handling CAB-O-SIL

CAB-O-SIL is an extremely fine and lightweight powder that can become airborne easily. Add the material slowly when mixing and avoid creating unnecessary dust.

Use appropriate personal protective equipment and review the current Safety Data Sheet before handling or use.

Need Help Choosing a Fiberglass Filler?

Not sure whether you need Cabosil, CAB-O-SIL, Q-Cell or another fiberglass filler? Contact Fiberglass Florida and let us know what resin you are using and what you are trying to accomplish. We can help you select the right thickener or filler for your fiberglass, marine or composite project.