A cat has three main types of cat hair and whiskers The hair types can
overlap in appearance:
All cat hair molts. This happens all year long and seasonally
(summer). Molting affects males and females. The winter coat is
slightly longer than the summer coat. The descriptions below apply to
longhaired and shorthaired cats alike. The extended period of growth
accounts for the longer hair. The slower rate of growth as opposed to
period accounts for the ultra short coats of the rex cats.

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Guard
hairs
These are the top coat with the awn hairs. These are normally straight
and they taper to a straight point. These are the longest hairs. They
constrict in diameter where the hair enters the skin. They thicken
inside the skin (subcutaneously).
Awn
hairs
These serve as a protective layer to the soft down hairs. They also
have a sensory function. These are thinner than guard hairs and thicken
near the tip of the hair before tapering to a fine point. The
thickening near the tip is called subapical swelling for the
technically minded. These hairs vary the most of the three types
of
hair.
Some are similar in thickness to the guard hairs and some are similar
in thinness as the down hairs (awn-down hairs). They sometimes have an
almost imperceptible the subapical swelling referred to above.
These are the second longest hairs. They constrict in diameter where
the hair enters the skin. They thicken inside the skin (subcutaneously).
Down
hairs
These are the undercoat. These serve as an insulating layer protecting
against heat loss. They are the thinest and finest hairs of the three
types. They are the same diameter throughout the length of the hair.
They are undulating.
These are the shortest cat hairs. This may in part be due to the
crimping of these hairs. Crimping means cat hair that has become wavy.
They constrict in diameter where the hair enters the skin. They thicken
inside the skin (subcutaneously).
Whiskers
They are called vibrissae. They have a very sensitive super tactile
function. These are very special and I have built a short page on these
hairs. See
Cat
Whiskers.
From
cat
hairs to home page
Source: Robinson's
Genetics for Cat Breeders & Veterinarians (4th Ed.)