Milling was started in France and meant the soap was run between steel bars and smoothed and compressed. Triple milled soaps actually go through this process 3 times.. or use 3 rollers... French Milled soap can only be bought in France, but anyone can 'mill' soap, just not call it French Milled. French milled soaps are definately considered to be the best..
I took this article from an Austrailian soap companies website as I thought it was very good in explaining what 'milled' means... here is the website... http://www.soapsolutions.com.au/
So what is So Good about French Triple Milled Soaps and what does it mean?
French Triple Milled Soaps are very much smoother to use than normal soaps and produce a more creamy, luxuriant lather more quickly that normal Soaps with a very even colour.
When soap is made it is dried prior to being turned into soap bars. During this drying process the soap turns into crystals and these crystals, which vary in size, can produce a quite gritty and rough base when made into soap bars.
True French triple milled soaps are passed 3 or more times through a heavy duty 3,4 or 5 roller mill. This repeated milling of the soap crystals crushes the soap crystals turning them into an extremely fine and smooth paste, prior to being turned into bars. This process also ensures that the soap colours and additive are homogenously spread through the soap bar.
French triple milling also means that all the bars in a batch are the same colour with no streaking even with heavily coloured soap
Some soap plants have a single roller mill not 3 roller mills in their process line. However a lot of them are cheap Chinese and Indian made mills that are very small and lightly built which means they are unable to apply the high pressures on the rollers that is required to produce High Quality Soaps.
I hope this helps in learning about soaps...