The thick, longitudinally cracked cork layers of the gray-brown trunk bark are characteristic of the cork oak. The cambium of the smooth bark of young trees forms a cork layer very early on, which can be thick. The light and spongy cork fabric shows vertical cracks and is white on the outside and red to red-brown on the inside. After the cork has been harvested, the trunk appears reddish brown, but later it is significantly darker. The wood is ring-pored, has a brown heartwood and a light reddish sapwood. The cork oak develops a taproot that reaches a depth of and from which several meters long, horizontally running side roots extend. The trees can reach over 400 years old, and harvested specimens can be 150 to 200 years old.