PLYCO foam Products POLYSEAL sill plate sealer is made from a lightweight polyethylene foam. By filling irregularities between the sill plate and the foundation, air infiltration is significantly reduced to provide savings on heating and air conditioning costs. Its durable, moisture resistant characteristics aid in the prevention of water and insect intrusion, two of the leading causes of sill plate rot. Discover the POLYSEAL advantage and close the gap on energy leaks.