A tortillion is nothing more than a piece of rolled paper used as a blending tool.  The softness or hardness of the tortillion is controlled by the type of paper you choose to make it out of.  I have never liked to use a finger or a blending stump on a drawing because it always looks like a big smudge when you are finished.  I started using a tortillion a few years ago when I was trying a new drawing technique.  I looked all over to purchase them and they were hard to find and expensive.  I took a few apart and figured out how to make them.  When I have students who want to blend with their fingers I show them how to make a tortillion.  Remember it is tortillion and not tortilla.  I always have students who ask me to show them how to make a tortilla.  I tell them we are drawing and not making Mexican food.  Finally a use for all your scrap paper.
 

 

These are the measurements I use.	Use different types of paper.
Start with a small fold in the corner.  Keep it at an angle and fold at least two times before you start rolling it.  It takes awhile to get the hang of the fold but when you do its pretty easy.	Once you get the rolling going keep it at an angle.  This angle is what keeps the point small.  If the angle is not steep enough you will not get a point on the end.
Here is one that's almost finished.  Note that this tortillion has a nice point on the end.  It works better as a blending tool if its pointed.	The finished tortillion is held together with a small piece of masking tape.  If you want it to look professional looking just fold the top extra material back into the hole that's left on the top.
Here are three tortillions using different types of paper.  Try different types of material and see which you like the best.	Here is a small example of tortillion blending.  Top with just pencil blending and bottom with pencil and tortillion blending.  When your tortillion gets dirty clean it with a rubber eraser.