The pestblock great stuff sounds like there's some advertising hype in there, here's a response to a question. GREAT STUFF(TM) Pestblock Insulating Foam Sealant does not contain any pesticides. This product has a bitter ingredient added to the foam to 'deter' rodents. However, if determined enough, they can chew through this product. The Dow Chemical Company recommends putting steel wool or wire mesh in the opening first, then sealing it with GREAT STUFF(TM) Insulating Foam Sealant Products. Please feel free to contact our customer information group at 1 (888) 868-1183 Monday through Friday between 8:00am and 5:00pm EST and speak directly to a call center agent if you have further questions. Read Less