OK, I was on the other violin site, String Academy, and asked a question about bow hair. Here's an excerpt from Tom Baker of (Bakers Rosin of Florida) and I found it so interesting I had to post it here for all to absorb.

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 It's more complicated than you might believe, but this is something I know a little about.

The differences between horsehair which really matter for us are, surface structure and elasticity.

The surface structure of true Mongolian is far and away the most efficient at manipulating the strings because it has even, consistent striations that face in every direction and every angle.

Elasticity - In our case it's a test to see how far a type of horsehair will stretch before it becomes permanently deformed.

Chinese hair will deform at just 2 Newtons of applied force.

Mongolian does much better - 2.77 N.

For the record, there is no such thing as quality bleached hair.

As is with strings and everything else, there are many variables and no one type of horse hair leads in all the positive attributes, so we try to select one that leads in the most important areas...surface construction and Elasticity.

For example, Canadian hair has amazing elasticity and will stretch without deformation with as much as 4.53 N, but the surface pattern isn't as useful as is the Mongolian.

Because surface construction has a greater effect on what we perceive whilst playing, it therefore is more important than elasticity.

The quantity of hair used has mostly to do with the resulting feel of the bow.

The more hair, the more spongy feeling. The less hair the more bouncy the feeling. (under the same tension)

Generally speaking, most bows have too many hairs on them as far as I'm concerned.

Also, quantity has a variable...hair width.

Fine Mongolian has a smaller diameter than does coarse Mongolian and so 150 hairs of Mongo-fine will have about the same surface area as 125 hairs of Mongo-coarse, but both work out to about the same feeling as far as effect goes.