The types of hair are pretty easy to tell apart, not due to width measurements, but due mostly to the cross section shape and pigment granule distribution.
Negroid hair…
is thin and almost flat in cross section (tape like), with a tendency to very tight curls. Sometimes it grows in tiny clumps, called peppercorn hair. African hair grows the slowest, at about 0.9cm a day. It’s angle of growth is very small, nearly parallel to the scalp. In colour, it is nearly always black in Africans. The only time you’ll see negroid hair of a different colour is if the individual is an albino, or has European ancestry, or if they dye it. Naturally coloured African hair has densely distributed pigment granules (hair shaft may be opaque) that are arranged in prominent clumps. The hairs also twist irregularly about their longitudinal axis, it has been described as a twisted oval rod.
Caucasian hair..
is a slightly irregular oval shape in cross section. It can to ruler straight, curly as an Africans, and every degree of curl between. It has the widest range of colours; black, auburn, shades of fair and brown to a near white blond. The hair grows out of the skull at an oblique angle, at a rate of about 1.2cm a month. the pigment granules are sparse to moderately dense with fairly even distribution .
Mongoloid hair..
grows the fastest at an average of 1.3cm a month. Its is more circular in cross section, although not perfectly regular. It grows out of the scalp at a right angle. The pigment granules are densely distributed and often arranged in large patchy areas or streaks. it is nearly always black.
Various links on racial variations of hair.
What is human hair. A light and scanning electron microscopy study
HAP Forensics Human Hairs Identification
Microscopy of Hair Part 1: A Practical Guide and Manual for Human Hairs
All three hair types under an electron microscope. The shape difference between African and European hair doesn’t show well here though.
An interesting exception to the Asian hair average is Ainu hair, which I have seen described as Caucasian in cross section. it’s also reputed to come in dark brown and a reddish brown colour.
Mathilda's Anthropology Blog. 
dis is facinating add more things to dis website
…interesting on the ainu, neander had
reddish brown hair. ainu were jomon?/
yomoni(N)=groom(pick nits out of hair),
e.g., yomozai(J)=hair tonic, yomu(J)=
compose: read(devour)carefully,
yomo(J)=shear sheep, jomozai(J)=
depilatory. i imagine they were,
and hairy. grooming begins the long trail
to what we know as civ, ornament, language,
deification, tzotzoyotia/society, awareness
of self and teotl/theother/el otro(sp/note
all the letters of teotl present).
I would like to know why many people are very blond as children, but then get darker hair as they grow older.
I was blond as I could be as a child, but by the time I was 13 my hair got darker. Now in middle age, my natural haircolor is a mouse brown, however it easily becomes light blond with just a 15 minute application of cheap blond hair color or with a few hours of sun exposure. You will also notice that with natural blonds the hair at the nape of the neck can be very dark….kind of strange.
If anyone knows why our hair color gets darker as we age….please email me and let me know.
On African Hair, your entry reads that black hair grows at “0.9cm a day”. I’m sure you mean “0.9cm a month”…
Hello,
thanks for the most informative info. I had seen some of these photos before but not in a study on hair. I did notice not much was from the old kingdom. Is it that they just haven’t gotten to it yet? And do you have any idea when they will?
I’m mostly interested in old kingdom. Thanks
I’m filipino (so primarily mongoloid), though I have Spanish and Indian ancestors somewhere down the line (caucasoid). It’s interesting because I also have a nephew born from both filipino parents with caucasian ancestry five generations back.
He has shockingly white-blond hair, and not an albino either. His features are entirely that of his dad and my sister (typical filipino, somewhat a cross between asian and latino features), but his hair is very unusual, given that I think asian genes are usually dominant (me for example, exhibit mostly asian features, despite having half spanish grandparents). But then again my sis has dark brown hair, like most of us in the family, in contrast to the pure black hair of the pure ethnic mongoloids in the far east. It will get darker as he ages of course, but it’s still interesting.