XLB invests in basic materials companies from the S&P 500, these would include companies in the chemicals, metals and mining, paper and forest products, containers and packaging, and construction materials industry. Its limited selection universe means it is heavily concentrated, and individual holdings must be taken into consideration before investing in this fund. Not surprisingly, XLB favors large-caps. Components of the index are all picked by the index committee, and weighed by free-float market capitalization, subject to a cap to ensure diversification requirements. Index rebalancing occurs quarterly. Prior to Dec. 1, 2025, the fund name did not include the Issuer's name, State Street.