Some readers have asked if other fixed income asset classes could be just as effective as long term treasuries for an equities portfolio in hedging an equities book (discussed here). Here the comparison is made to municipal bonds, investment grade corporate bonds, and HY corporate bonds. Long term treasuries are still superior in reducing the portfolio volatility - at least based on the last couple of years. That's because muni and corporate spreads tend to be inversely correlated to equities, reducing the hedge effectiveness of these instruments.
Again, the x-axis is the percent of the portfolio invested in the S&P500, with the rest of the portfolio being in one of the fixed income asset classes. The y-axis is the combined portfolio daily volatility over the past two years.
That is the reason investors are willing to take asymmetric risk and dismal current yield to hold long term treasuries. Whether this relationship holds going forward remains unclear. A scenario in which both treasuries and equities sell off some time in the future is not unrealistic.