3M Fire Barrier Sealant CP 25WB+ - Intumescent Firestop Sealant

In this review the 3M Fire Barrier Sealant CP 25WB+ is evaluated for contractors, facility managers and serious DIYers who need a reliable, code-compliant firestop sealant. The bottom line: it is a one-component, latex-based intumescent sealant that makes firestopping straightforward and effective, with the single biggest reason to buy being its ability to expand when exposed to high heat and maintain a fire penetration seal for up to 4 hours. This review focuses on real-world use, ease of application, and how well it meets building code needs.

Key Features

• Building code compliance: Designed to seal openings through fire barriers where mechanical services pass, helping projects meet listed through-penetration systems.
• Intumescent expansion: Capable of expanding a minimum of three times its dried volume when exposed to temperatures above 1000F, which helps maintain the integrity of a penetration seal.
• Multiple UL systems: Listed in hundreds of UL Firestop systems with up to 4-hour ratings, providing flexibility across wall, floor and floor-ceiling assemblies.
• Versatile applications: Works on HVAC ducts and vents, pipes, blank openings, cables and busways, making it practical across commercial, industrial and residential jobs.
• Easy application: One-component, sag-resistant formula that applies from a cartridge with no mixing required and cleans up with water when fresh.

Who It's For

This sealant is best for electricians, plumbers, HVAC installers, general contractors and maintenance teams who need a proven firestop material that integrates with established UL systems. It suits projects where rated penetrations must be maintained and where a latex-based, non-sag product simplifies on-site work.

It is less suited for cosmetic visible beads where a perfectly smooth finish is required without sanding or for users who insist on solvent-based sealants for specialty substrates; anyone uncertain about listed system requirements should consult a firestop engineer or follow a specific UL assembly prior to installation.

Pros & Cons

Pros

• Easy to apply from a cartridge and compatible with a standard caulking gun for faster installation.
• Adheres well to common substrates such as drywall and many plastics, giving a dependable bond at penetrations.
• Provides both fire and smoke control, expanding under heat to maintain a seal during a fire event.
• Listed in many UL systems and rated up to 4 hours, which simplifies specifying for rated assemblies.

Cons

• Can be messy during application and cleanup requires prompt water washing while fresh to avoid hardened residue.

Specifications

Product	3M Fire Barrier Sealant CP 25WB+
Volume per cartridge	10.1 fluid ounces
Package	Pack of 12 cartridges
Base	One-component latex-based intumescent
Fire rating	Listed in UL systems up to 4 hours
Expansion	Expands minimum 3x dried volume above 1000F
Applications	HVAC, pipes, cables, blank openings, through-penetrations

Our Verdict

The 3M CP 25WB+ is a practical, code-oriented intumescent sealant for professionals who need a reliable firestop that is easy to apply and listed in many UL systems. Its expanding capability and water-cleanup while fresh make it a good value for commercial, industrial and residential projects that require rated penetrations, provided installers accept some mess during application.

Frequently Asked Questions

Is this sealant suitable for both walls and floors?
Yes. It is used in rated wall, floor and floor-ceiling assemblies and is listed in through-penetration systems for those applications.

How long does the firestop rating last once installed?
When installed per a listed system this sealant contributes to firestop solutions with ratings up to 4 hours.

Can the product be cleaned up easily?
Cleanup is straightforward with water while the sealant is fresh, but it becomes difficult to remove once cured.