There are many reasons for coating FDM® parts. These include UV protection, sealing, shielding or surface modification, but painting FDM parts for an aesthetically pleasing
finish is the most common. Painting brings a product to life by adding depth, contrast
and character. This is true for concept models, marketing samples and finished goods.
For  product  development  and  many  production  applications,  paint  completes  the desired  look  and  feel.    With  a  little  know-how  and  a  touch  of  patience, models, prototypes and parts can look like production parts (Figure 1). 

The following instructions are for creating top-quality painted parts.  For applications
that do not require this level of finishing, skip any unneeded steps. A good paint finish
traditionally starts with sanding and filling.
Fillers: Used for surface preparation when moderate to severe surface filling is
  required. Use filler when the part has excessive layering or when there are surface
  voids that primer will not fill.
Primers: Used for surface preparation when minimal surface filling is required, or to
  improve paint adhesion.
Paints: Used to provide the desired color, texture and luster.

For more information, download the full best practices document here.

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