Unfortunately, this product doesn't act like a vapour barrier. I hope this helps.

Dow only recommends the use of Great Stuff (TM) Window and Door to be used in this application. The makers of GREAT STUFF™ are setting the standard for the method that windows and doors should be installed. GREAT STUFF™ Window & Door foam sealant is exclusively formulated to air-seal the gap between a window or door frame and its rough opening. All GREAT STUFF™ products are polyurethane-based and offer superior performance advantages over latex products.

Window and door manufacturers such as Pella** Corporation have tested and endorsed GREAT STUFF™ Window & Door.

Proprietary low-pressure formula designed not to bow or bend window and door frames
Ideal for filling or sealing other areas where low-pressure flexible foam is desirable
Forms a durable, airtight and water-resistant bond
Quick cure time. Tack free in eight minutes, trims within one hour
Paintable, sandable and stainable
Yellow colored foam
Repels/deflects water
Conforms to ASTM & AAMA standards
One 12 oz. can of Window & Door foams up to four to six average sized residential windows (36’ x 60”, 3/8” wide gap, and 1” deep)
Provides real insulation value which complements energy efficiency of the window or door. Greater insulating value than chinked fiberglass or caulk
Flexible foam permits expansion and contraction
Soft, pliable foam is forgiving, easier to remove if gap is overfilled. Cured foam can be stuffed back into the gap without trimming.
GREAT STUFF™ Window & Door meets or exceeds all industry standards for the installation of exterior windows, doors and skylights.

Great Stuff (TM) products are not approved in Canada as a fire block product. For more information on the Great Stuff (TM) products please contact Dow Chemical at 866-583-2583.

You can request an up to date MSDS for any Great Stuff ™ product by calling Dow Chemical at the phone number printed on every can. That number is 888-868-1183, or 866-583-2583.

Great Stuff (TM) should not be used around any heater, furnace, fireplace or recessed lighting fixture where it contacts heat conducting surfaces. The foam will burn if exposed to open flames or sparks from high energy sources such as a welding torch, and it will start to thermally degrade if exposed to temperatures above 240F for long periods of time. The cured foam can handle ambient temperatures up to 240F before thermal degradation starts, which means the foam will break down and could begin to burn. Please make sure that any surface that the Great Stuff foam comes in contact with stays within the temperature limits stated..

Purchasing the Great Stuff (TM) Pro over the consumer Great Stuff (TM) may be appealing because the simplicity of foam application with PRO Series foam dispensing guns (PRO 13, PRO 14 and PRO 15). Use GREAT STUFF PRO™ Gun Cleaner to simplify cleanup of uncured polyurethane foam from dispensing guns and work areas. Also the Great Stuff (TM) Pro can be stored on the Pro Gun when shut down properly for up to 30 day and restarted. The consumer Great Stuff (TM) product is a one time use product and will seal itself shut if left unused one started in 2 hours.

Great Stuff (TM) can be used to fill holes created by insects and rodents. The foam does not contain any poisons and does not have any nutritional value so the insects and rodents can return and chew through the foam, depending on how determined they are, they can chew through the foam to gain entry into your home once again. One hint is to place steel wool into the holes before applying the Great Stuff (TM) foam, this may deter the insects and rodents from continuing to chew through the foam.