SOFT PASTELS are the purest form of artist color, made almost exclusively from pure pigment with only enough binder to allow them to be formed into useable sticks. Pastels vary from hard (Nupastel) to very soft (Schmincke) with many variations in between.
The extensive color lines like Sennelier allow artists a choice of many subtle color variations. If a handmade color chart is available for a line of pastels, it is listed below the individual pastel price.

COMPARING PASTEL LINES
We are often asked to compare the different lines of pastels to help customers decide which pastels they should purchase. Factors such as color range, physical characteristics (hard/soft, square/round, big/small) and economics all enter into which is the right pastel for you.  The one area in which we can give a ‘general’ classification is softness.Keep in mind that this is a general classification - some pastels vary within the line and many of these are so close it’s difficult to rate one softer than the other. 
Listed in order of softness (#1 being the softest)