Foam Gap Filler and Fire Seal
Great Stuff Pro Gaps & Cracks (and Fire block)
GREAT STUFF PRO™ Gaps & Cracks Insulating Foam Sealant meets the
following fire blocking standards:
• ASTM E84 – Standard Test Method for Surface Burning Characteristics of Building Materials
• ASTM E814 (modifed) – Standard Test Method for Fire Tests of Through- Penetration Fire Stops
• CAN/ULC S102 – Method of Test for Surface Burning Characteristics of Building Materials and Assemblies
Note that depending on your particular code jurisdiction there may be a limit on the size of hole that the foam can fire seal. It could be limited to 1/2" gaps in some areas.
http://www.ebay.com/itm/Dow-Great-Stuff-Pro-Gaps-and-Cracks-24-oz-Gun-Foam-Case-of-12-341557/121858426621?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20131003132420%26meid%3De7c7298c18c44fc4822b357ac437b508%26pid%3D100005%26rk%3D4%26rkt%3D6%26sd%3D121858426726 $105 for 12 ($8.75 each)
http://www.amazon.com/Dow-Great-Stuff-Cracks-341557/dp/B0013WME6C $8.99 + $4.50 shipping (luckily shipping cost does not go up linearly)
Where you have lots of gaps to fill in one go then it is actually less expensive to use the one-use cans.
Lowes has it for $3.68
I use three different types of foam depending on how much expansion
No expansion - Foam Adhesive
Small expansion - Foam Windows and Doors
Large expansion (and fire seal) - Foam Gap Filler and Fire Seal
GREAT STUFF PRO™ Gaps & Cracks - As the first foam sealant to be recognized as a fireblock, GREAT STUFF PRO™ Gaps & Cracks inhibits the spread of flames through concealed spaces. It’s a minimal-expanding, single component polyurethane foam sealant for general purpose building envelope air sealing.