Singlewall Carbon nanotube - SWCNT
Multiwall Carbon nanotube - MWCNT
When the material is made (as-produce) the nanotubes comes straight out of the reactor with the approximate concentration of  95% MWCNT  ( 90% in the case of SWCNT) nanotube vs. non-nanotube material. These nanotubes are then processed and purified.  This step yields an increase in purity of the tubes which are sold as "Purified Open Material".  This step uses a Heat and Acid Wash process, which removes the non-nanotubic material.  (Non-Nanotubic material is usually comprised of amorphous and graphitic carbon, and metal catalyst, Nickel-Yttrium, Iron or other metals).  Also process may shortens the nanotubes by “end eroding” during the acid wash which removes the ends of the nanotubes.
A summary of the steps follows:

      . Heat nanotubes in air to 300C to expose the carbon surface and oxidize the metal catalyst. 
      . Sonicate and wash in nitric acid and/or HCL  to remove the metal catalyst, amorphous carbons and to open the ends of the nanotubes. 
      . Clean with solvent and hot air dry.  (acetone, ether and etc.)