I'm not sure who invented the Viva Paper Towel Method of smoothing, but it works perfectly and we've been doing it for years! Viva brand towels have no impressions or quilting, and so they can be used to gently smooth over freshly crusted buttercream. You may be able to find these in your local grocery store--Or, any non-quilted paper towel or napkin should work in the same way.
(via Amazon): 6 big rolls = 8 reg. rolls (Compared to Viva Choose-A-Sheet Regular Roll).--- Strong & soft like cloth.--- Choose-a-sheet. Viva Towels work like cloth to stand up to any cleaning job.