From Mladen Rakic:

Bollinger Bands consist of a N-period Moving Average (MA), an Upper Band at K times an N-period standard deviation above the Moving Average (MA + Kσ), and a Lower Band at K times an N-period standard deviation below the Moving Average (MA − Kσ).

This version does not use standard deviation for Upper and Lower Bands, but uses the EMA deviation. That makes it faster in the response to market volatility.