From a technical paper issued by the Wool Board some time ago it appears that pilling is one of knitwear's problems which cannot be completely avoided. Pilling occurs more readily in garments made from high quality yarns especially if the garment is subjected to friction in wear.
  The risk of pilling can be reduced by using coarser quality yarns or by knitting with a tighter tension but these methods can produce a less desirable "handle" than is expected in a high quality garment.
  There is little the manufacturer can do to prevent certain garments from pilling and it can occur on the very best garments but if removed when first noticed in many cases further pilling will not occur.
  Pilling is not a fault of the garment but is caused by high quality natural fibre construction.