Ductility is the amount of strain a seal can withstand before brittle failure and the loss of top seal integrity. Rocks with an extremely high ductility can deform without brittle failure. On the other hand, rocks with low ductility can accommodate only a small amount of strain before fracturing. A seal can be brittle but unfractured; a seal can be ductile but fractured. Fracture depends upon whether the strain exceeds the seal ductility.