The itchy sensation from fabrics results from our
skin being irritated by the ends of the fibers
which make up the fabric; it is similar to being
lightly pricked by many tiny needles.
buckling load of the protruding fibers, given by
P_E = pi2*(E*I) / (4*L2)
(E = Young's modulus[stiffness], I
= moment of inertia
[= pi/64*diameter4 for circular rods],
L = length of
fiber protruding from fabric), has been identified
as the dominant parameter for causing the "itchy"
sensation ; higher P_E means an itchier fabric.
From this expression, we can see that fabrics made
of stiff (high E), thick (large radius -> high I),
short (lower overall length will limit the
protruding length L) fibers will feel itchier. If
you look around at the properties of various
fabrics, you should find that they follow these
As an example, a wool used to make carpet
has shorter fibers and fiber diameters of ~40 µm.
Carpets, correspondingly, are quite coarse and
itchy. On the other hand, a high quality Merino
wool can have a fiber diameter of 20 µm or less,
and is soft and comfortable. Microfiber
made of synthetic fibers that are even finer, less
than 10 µm, and are very soft.
Another aspect to consider is the roughness of the
surface of the fibers. Fibers with rough surfaces
will prevent the movement of surrounding fibers,
reducing L, and can also act as additional short
protrusions that prick skin and cause irritation.
Here is an image of several fibers under a
Coarse wool is indeed very rough,
while fibers that are considered very soft not
itchy (e.g. cashmere, silk, and the synthetic
polyester) are very smooth.