STI Firestop SpecSeal® Composite Sheets

Lightweight, Thin, and Easy to Work With

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What's special about these firestop sheets?

  • Panels are intumescent up to 15 times their original size for excellent firestopping of large or small openings
  • Once activated, these sheets form a dense insulated char, which reduces the transfer of heat and smoke
  • 50% lighter in weight and approximately 1/2 the thickness of standard composite sheet products for easy installation and handling
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UL ClassifiedFM Approved

Composite sheets have long been a favorite for firestopping large openings where a clean, neat finish is required. In addition, these sheets provide an excellent exterior surface. You may use the composite sheets with other STI Firestop products to seal penetrations through fire-resistance rated walls and floors for metallic and non-metallic pipes, insulated pipes, cable trays, cables, conduits, or blank openings.

STI-CS1628 SpecSeal® Composite Sheet 16" x 28" 16" x 28" x 0.1"
(41cm x 71cm x 2.5 mm)
4.4 lbs
(2 kg)
STI-CS2436 SpecSeal® Composite Sheet 24" x 36" 24" x 36" x 0.1"
(61cm x 92cm x 2.5mm)
8.4 lbs
(3.8 kg)
STI-CS3636 SpecSeal® Composite Sheet 36" x 36" 36" x 36" x 0.1"
(92cm x 92cm x 2.5mm)
12.6 lbs
(5.7 kg)
STI-CS3641 SpecSeal® Composite Sheet 36" x 41" 36" x 41" x 0.1"
(92cm x 104cm x 2.5mm)
14.4 lbs
(6.5 kg)
STI-CS2852 SpecSeal® Composite Sheet 28" x 52" 28" x 52" x 0.1"
(71cm x 132cm x 2.5mm)
14.2 lbs
(6.4 kg)

These products protect openings of any shape in common construction work against fire, smoke, and combustion by-products. Another benefit to this type of firestop is that no maintenance is needed as there might be with other choices; however, it is recommended that any new openings or jobs be inspected to ensure that all remained sealed.

  • Durability built in: made of an intumescent layer bonded to a galvanized steel sheet, reinforced with steel wire mesh and covered with aluminum foil
  • Easy to cut using standard sheet metal cutting tools to size your composite sheets to specs
  • Can be used with other SpecSeal® or EZ Path products by STI
  • UL Classified
  • Tested to ASTM E814 (ANSI/UL 1479) for up to 2 hours
  • Specifically created for use in medium- to large-sized openings
  • Excellent for use in both floors and walls because it is lightweight enough for handing and hanging
  • Paintable for blending with current décor



  • Seal penetrations through fire-rated walls and floors
  • Metallic and non-metallic pipes
  • Insulated pipes
  • Cable trays
  • Cables
  • Conduits
  • Blank openings
  • Suitable for clean room/area environment



Item Composite Sheet
Material 31 AWG, Steel Sheet, Steel Wire Mesh, and Aluminum
Mounting Floor or Wire
Fire Rating 2 hours
ASTM E814 (ANSI/UL 1479) Up to 4 hour ratings for penetrations in walls and floors
ASTM E814 Electrical Circuit Protection Systems for Cable Trays 1 hour UL Classified Systems
Surface Burning Characteristics Flame Speed 5
Smoke Development 50
Nominal Thickness 0.1 inch (2.5mm)
Nominal Weight 1.4 lb/ft² (6.9 kg/m²) Intumescent
Expansion Begins 350° F (177° C)
Volume Expansion 15 X (typical free expansion)
Max. In-Service Temperature 130° F (54° C)
Radiation Exposure Unaffected
Shelf Life No Limit
VOC Content n/a
STC Rating 55






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