Duct seal putty is a gray, permanently soft, non-toxic compound used to seal out air, moisture, dust, and other contaminants.

It adheres well to most clean, dry surfaces and doesn't dry out, corrode metals, or react with plastic materials. It also has no adverse effect on human skin and is non-toxic.

Applications

Rainbow Duct Seal Putty is used primarily by the building industry, and specifically by the electrical trade, to seal around electrical boxes, flashings, service mast entries, and more. It can be shaped by hand to any form and reused if necessary.

This duct seal compound has countless other applications in the refrigeration, heating and cooling, plumbing, and metal fabrication fields. It also serves as an excellent general-purpose sealant around the home. The putty may be painted immediately after application and will not bleed through the dry paint.

Features & Benefits

• FDA Approved: Rainbow Duct Seal Putty is composed of materials that meet FDA standards as listed in CFR Title 21. This makes it suitable for use in environments where incidental contact with food packaging or handling surfaces may occur, such as cold storage, food service, and processing facilities.

• USDA Acceptable: Chemically acceptable for use in federally inspected meat and poultry processing plants. It complies with USDA regulations for non-food contact applications in areas subject to routine sanitation and inspection protocols.

• Dielectric Strength: Tested to ASTM D149-64, the insulating putty provides effective electrical insulation with a dielectric strength of approximately 200 volts per mil (10,000 volts total), making it ideal for sealing around boxes, fittings, and conduit penetrations.

• Utility-Strength Sealing Power: The putty blocks out air, moisture, and dust in demanding environments to deliver long-term sealing performance even in overhead, vertical, or irregular applications.

• High Performance Chemical Resistance: Excellent resistance to water, alcohols, and mild acids and bases. While not rated with a formal waterproofing certification (for example, IP or ASTM water submersion standards), Rainbow Duct Seal Putty has been extensively tested for moisture resistance and is proven to maintain performance in wet, humid, and weather-exposed environments. This means it won't soften, dissolve, or break down when exposed to these substances.

• Vehicle Bleedout: None. The insulation putty retains its form without oozing or staining surrounding surfaces.

• Non-Corrosive: The compound won’t initiate or accelerate corrosion, making it safe to use on copper, aluminum, galvanized steel, and other metals often found in electrical, plumbing, or HVAC systems.

• Non-Irritant: Does not irritate the skin or eyes during normal use.

• Paintability: Yes, paint may be applied immediately after installation. The compound does not interfere with adhesion or curing and will not bleed through or discolor surface coatings over time.

• UV Inhibitors: Contains a pigment that absorbs UV and converts it to heat to reduce polymer breakdown. This, together with antioxidant inhibitors, preserves the chemical structure of the sealant, extending its life in outdoor or sun-exposed areas. And because the base polymers themselves are already UV-resistant, the product performs reliably in exposed exterior environments.

Expanded Use Cases

• HVAC Systems and A/C Unit Insulation: The putty is commonly applied to seal around refrigerant lines, wall sleeves, and duct penetrations. It helps maintain thermal performance by preventing air and moisture infiltration at junction points where rigid insulation is not effective.

• Sealing Electrical Boxes and Conduits: Electricians use it to seal around junction boxes, knockouts, and conduit entries. It keeps out moisture, dust, and insects, and holds its shape even when applied overhead or in tight spots.

• Industrial and Commercial Settings with Heat Exposure: This thermal insulation putty remains intact near heat-generating equipment and does not slump or degrade when used around motors, exhaust systems, or process piping.

• Outdoor Applications and Water-Exposed Settings: The putty performs well in exposed or high-humidity areas, including building exteriors, crawlspaces, and utility enclosures. It resists water intrusion, withstands freeze-thaw cycles, and maintains adhesion and flexibility when subjected to direct sunlight and weathering.

Why Choose Rainbow Duct Seal Putty Over Other Options?

Unlike many generic putties that dry out, stain surfaces, or contain skin irritants, Rainbow’s formula is non-toxic, reusable, and corrosion-resistant. It performs in extreme temperatures, adheres to a wide variety of materials, and requires no additional sealers or protective coatings, which makes it a cleaner, safer, and longer-lasting solution.

Technical Highlights