Emphasizing density and volume:
* A cascading waterfall of hair.
* A thick, lush forest of hair.
* A mane of hair like a lion's.
* Hair so thick it could suffocate a pillow.
* A cloud of hair, soft and abundant.
Emphasizing texture and strength:
* Hair like woven silk, strong and lustrous.
* A thick, rope-like braid of hair.
* Hair as sturdy as a cable, unyielding and strong.
* Hair that feels like a dense, plush carpet.
* Hair that stands up on its own, defiant and powerful.
Emphasizing beauty and health:
* A crown of thick, healthy hair, shining with life.
* Hair like a rich tapestry, intricately woven with beauty.
* A halo of thick, vibrant hair, framing a youthful face.
* Hair that flows like a river, smooth and healthy.
* A blanket of hair, soft and inviting to the touch.
The best metaphor will depend on the context and the specific image you want to evoke.