Bamboo Barrier is a diversion-type control method with a smooth surface on the side facing your bamboo planting. It is made from HDPE high-density polyethylene. Superior to metals because it will not rust and is easier to install. Bamboo roots typically travel in the first 12 in. of topsoil. The barrier is sold in 24 in. 30 in. and 36 in. to provide extra protection from stray growth. BAMBOO SHIELD is impermeable to water as well which acts as a water barrier. Plastic thinner than 30 mil has been shown to crack when ground temperatures 24 in. D get below minus 15F. This would be extremely cold and the thickness greater than 30 mil does great at handling very cold temperatures without damage. The plastic barrier has a better chance of not cracking when frozen like other materials. Even concrete will freeze and crack over the years. Driveways are poured 4 in. D to 6 in. D to allow heavy vehicle passage and parking. Seldom are driveways seen without cracks. Concrete was used many years ago Byron Agriculture Station in Byron Georgia as a below-ground barrier system and found to crack below the frost line allowing bamboo rhizomes to emerge through to the other side. One of the many myths of bamboo is its ability to crack solid concrete. While a clumping type bamboo may do this given enough years a running type bamboo just runs and does not usually apply the outward pressure of a clumping bamboo or hardwood tree.