Nelson FSP™ Firestop Putty

Moldable, Reusable, and Instant Firestopping


What's special about moldable firestop?

  • Constructed of a blend of organic and inorganic intumescent materials that expand with extreme heat to seal voids from exposure to fire and smoke
  • Pre-mixed material is ready to use right out of the box, so it requires no additional blending, and saves time on the jobsite
  • Hand moldable, so it requires no specialty tools for installation or adhesion
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Nelson FSP™ is an excellent way to create an instant fire seal. This easy to use mixture can be pressed in place by hand, and requires no special equipment or processes, so installation and cleanup are a breeze. FPS™ is the perfect solution for retrofit applications, and situations in which frequent cabling changes take place.

Part #DescriptionDimensionsQuantity Per PackWeightPrice / Pk
NFS-AA458Nelson FSP Moldable Putty Pad6" x 7" x 1/8"10.625 lb
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  • Reusability is ideal for making changes to your cabling throughway, and convenient for retrofit installations
  • Putty stays pliable at all times and doesn't set, so it can be easily removed and reapplied
  • Requires no curing or drying time
  • Weather resistant for added durability and corrosion resistance
  • Acoustically tested to reduce the transmission of noise and vibration
  • For faster installation, no cable derating is needed
  • 3-hour rating complies with ASTM E119 and UL263 for building construction materials
  • Available as an easy to carry and store putty bar, or as putty pads


Ideal for filling voids on or around:



  Physical Properties
Color Tan
Density 0.049 lbs / in3
Consistency 7.00mm (Penetrometer)
Activation Temperature 500° F (260° C) Max.
Application Temperature 40° F (4° C) to 110° F (43° C)
Dielectric Strength >356 v/mil
STC Rating 54
  Test Compliance
  Flame Spread - 5
  Smoke Developed - 10
ASTM E814 and UL 1479
ANSI / UL 263
Underwriters Laboratories, Inc "Fill, Void, or Cavity Material (XHHW)", FM, ABS, and USCG City of New York, New York, Department of Buildings
MEA 135-00-M
MEA 196-84-M Vol 3
  Storage & Handling
Nelson FSP™ should be stored indoors. Long term storage temperature: 140° F (60° C) maximum. There is no indication of shelf-life limitations. Partially used bars should be re-wrapped in their original packaging before being stored.






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