This week, 4 Chemicals stocks are improving their overall rating on Portfolio Grader. Each of these rates an “A” (“strong buy”) or “B” overall (“buy”).

This week, LyondellBasell Industries NV (LYB) pushes up from a C to a B rating. LyondellBasell Industries NV produces chemicals, fuels, and polymers used for packaging, clean fuels, durable textiles, medical applications, construction materials, and automotive parts. The company also gets A’s in return on equity and free cash flow. For more information, get Portfolio Grader’s complete analysis of LYB stock.

This is a strong week for Dow Chemical Company (DOW). The company’s rating climbs to B from the previous week’s C. Dow Chemical Company is involved with the manufacture and sale of specialized products and services, such as chemicals, plastic materials, and agricultural products, as well as property and casualty insurance and reinsurance business. The company also gets A’s in operating margin growth, earnings growth, and return on equity. For more information, get Portfolio Grader’s complete analysis of DOW stock.

Kraton Performance Polymers, Inc.’s (KRA) ratings are looking better this week, moving up to a B from last week’s C. Kraton Performance Polymers, Inc. produces engineered polymers and styrenic block copolymers. For more information, get Portfolio Grader’s complete analysis of KRA stock.

American Vanguard Corporation (AVD) improves from a B to a A rating this week. American Vanguard Corporation is a specialty chemical manufacturer that develops and markets products, such as chemicals for crops and animal protection, for agricultural and commercial uses. The company also gets A’s in operating margin growth, earnings growth, earnings surprise, and earnings momentum. For more information, get Portfolio Grader’s complete analysis of AVD stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.