Both the Bollinger Bands (gold) and Keltner Channels (purple) are trend following indicators with a volatility based envelope as you can see on the 60-minute chart below of SPY, the S&P 500 ETF. They are trend following because the directions of the Bollinger Bands are dictated by the 20-period SMA (Simple Moving Average) and the directions of the Keltner Channels follow the 20-period EMA (Exponential Moving Average). The bands for the Bollinger bands are a multiplier times the Standard Deviation above and below the 20-period SMA. The channels for the Keltner Channels are a multiplier times the ATR (Average True Range) above and below the 20-period EMA. The multiplier is usually 2 for both the Bollinger Bands and Keltner Channels. Since the Standard Deviation is “more volatile” than the ATR as you can see on the 60-minute chart below The Bollinger Bands cover a wider range, often the Keltner Channels are within the Bollinger Bands. For this reason some traders prefer the Keltner Channels over the Bollinger Bands. Another reason is that the 20-period EMA is more sensitive than the 20-period SMA. On the chart below both moving averages turned down and the price is below these moving averages, which is short-term bearish.