The VIX futures fair value is, instead, calculated by pricing the forward 30-day variance which underlies the VIX Futures settlement price. The computation of fair value is fairly complicated. For those of you who wish to delve deeper into the mathematics, more information can be found on the CBOE Futures Exchange website at http://cfe.cboe.com/education/vixprimer/Features.aspx
VIX futures price based on where the market expects to see the VIX on a given date in the future, i.e, the day the VIX expires. That estimate may or may not move on a given day with a move in the VIX. The further out in time the future is, the less it will track VIX moves.