For investors seeking to place money in U.S. Treasurys, there are a number of options for exchange-traded funds, or ETFs. Although Treasurys have paid low yields since the 2008 financial crisis, they offer significant portfolio diversification for investors to minimize risk to their stock holdings. Treasurys are not very correlated with the stock markets. U.S. Treasurys are also considered one of the safest investments available. The U.S. government has never defaulted on its debt obligations.

Investors should be able to find an ETF that holds Treasurys along the portion of the yield curve in which they wish to invest. The yield curve represents the maturity length of the Treasury. Most of the ETFs merely hold Treasurys passively. Thus, the expense ratios for these ETFs are very low. It is often easier for most investors to buy an ETF than to purchase Treasurys directly. This makes Treasury ETFs an attractive and low-cost investment. The iShares family of bond ETFs provides exposure to different sections of the yield curve. The following are four Treasury ETFs investors may want to consider.

iShares 1-3 Year Treasury Bond

The iShares 1-3 Treasury Bond ETF (NYSEARCA: SHY) holds Treasurys with maturities of one to three years, which is the short end of the yield curve. The fund had around $11 billion in assets and 81 holdings as of August 2015. It also has a dividend yield of 0.53%. This dividend yield is low since short-term Treasurys pay lower yields versus longer-term Treasurys.

The weighted average coupon for the holdings in the fund is 1.16%. The average weighted coupon is the average coupon rate of the holdings in the fund times the weighting of the bonds in the fund. The weighted average maturity is 1.82 years.

The benchmark index for the fund is the Barclays US 1 to 3 Year Treasury Bond Index. SHY has an average daily volume of around 1.8 million shares. It has an extremely low expense ratio of 0.15% and began trading in 2002.

SHY is appropriate for investors with a low-risk tolerance since the fund has very low volatility. The three-year standard deviation is 0.53%. The equity beta versus the S&P 500 is -0.03. This indicates the fund does not move with the stock market. It shows how SHY is good for the purposes of portfolio diversification. It can be used to balance out a portfolio of stocks with higher beta and higher standard deviations.

iShares 3-7 Year Treasury Bond

The iShares 3 to 7 Year Treasury Bond ETF (NYSEARCA: IEI) provides exposure to Treasurys with remaining maturities of three to seven years. The fund tracks the Barclays US 3-7 Year Treasury Bond Index as its benchmark index. IEI has 66 holdings with net assets of $5.6 billion, as of August 2015. The only holdings in the fund are U.S. Treasurys.

IEI has an average weighted coupon of 1.76%, with an average weighted maturity of 4.74 years. It has around 45 million shares outstanding with an average daily trading volume of around 365,000 shares and a daily dollar trading volume of $41.32 million. IEI has an expense ratio of 0.15%, similar to the other iShares Treasury funds.

The fund is appropriate for investors seeking exposure to this section of the yield curve. It has slightly higher volatility than the iShares 1-3 Treasury Bond ETF but also pays a greater dividend. The fund has an equity beta of -0.10 and a standard deviation of 2.74%. Like the other iShares funds, it can be used to diversify the holdings in a stock portfolio.

iShares 7-10 Year Treasury Bond

The iShares 7-10 Year Treasury Bond ETF (NYSEARCA: IEF) provides exposure to U.S. Treasury bonds with intermediate terms. This fund holds Treasurys further up along the yield curve with maturities between seven to 10 years. The fund had only 21 holdings with assets of $7.2 billion, as of August 2015. The yield is 1.93%, which is higher than SHY, due to the longer maturity of the fund’s holdings.

The weighted average coupon is 2.26%, with an average weighted maturity of 8.43 years. The effective duration of the portfolio is 7.6 years. The effective duration is the responsiveness of the price of a bond to a change in interest rates. IEF has a higher responsiveness to an interest rate increase due to the longer maturity of the Treasurys. The fund has an expense ratio of 0.15%. It has very high liquidity with an average volume of around 1.5 million shares. IEF began trading in 2002.

This fund is appropriate for investors seeking higher yields but who are also willing to accept greater volatility versus Treasurys with shorter maturities and shorter durations. Although the fund pays a higher dividend yield, it has a greater standard deviation. The three-year standard deviation is 5.26%. The equity beta is slightly negative at -0.14. Thus, the fund can still provide good diversification to a portfolio of stocks.

iShares 20+ Year Treasury Bond

The iShares 20+ Year Treasury Bond ETF (NYSEARCA: TLT) provides exposure to Treasurys with maturities greater than 20 years. The fund has 20 holdings as of August 2015, all of which are U.S. Treasurys. TLT has an average daily trading volume of 9.6 million, making it one of the most liquid Treasury ETFs in the market. The dividend yield is around 2.57% with a weighted average coupon of 3.39%. The average weighted maturity of bonds in the fund is around 26 years. The effective duration is 17.5 years.

TLT is appropriate for investors looking for greater yield than that available for bonds with shorter maturities. The greater yield comes at the expense of higher volatility. Investors must be able to withstand greater price fluctuations versus other bond funds. The three-year standard deviation is 11.6%. This is more than twice as much as the iShares 7-10 Year Treasury Bond ETF. Due to the longer effective duration, the fund has much greater sensitivity to changes in interest rates. It has a lower equity beta of -0.37. TLT does not move with the larger stock market. Thus, it may be the best fund on this list for diversification purposes.

Want to learn how to invest?

Get a free 10 week email series that will teach you how to start investing.

Delivered twice a week, straight to your inbox.