cork/bottle cork is formed from

The cork cambium or phellogen cells divide periclinally cutting off cells towards the outside and inside . The cells cut off towards the out side becomes suberised and dead . These are compactly packed in radial rows without intercellular spaces anda form cork or phellem.
Cork is impervious to water due to the suberin and provides protection to underlying tissues . the cells cut off from cork cambium towards inside add to the cortex and are called secondary cortex cells or phelloderm cells.