Investors interested in stocks from the Chemical - Specialty sector have probably already heard of Celanese (CE) and Ecolab (ECL). But which of these two stocks presents investors with the better value opportunity right now? Let's take a closer look.There are plenty of strategies for discovering value stocks, but we have found that pairing a strong Zacks Rank with an impressive grade in the Value category of our Style Scores system produces the best returns. The Zacks Rank is a proven strategy that targets companies with positive earnings estimate revision trends, while our Style Scores work to grade companies based on specific traits.Right now, Celanese is sporting a Zacks Rank of #2 (Buy), while Ecolab has a Zacks Rank of #3 (Hold). Investors should feel comfortable knowing that CE likely has seen a stronger improvement to its earnings outlook than ECL has recently. However, value investors will care about much more than just this.Value investors analyze a variety of traditional, tried-and-true metrics to help find companies that they believe are undervalued at their current share price levels.Our Value category grades stocks based on a number of key metrics, including the tried-and-true P/E ratio, the P/S ratio, earnings yield, and cash flow per share, as well as a variety of other fundamentals that value investors frequently use.CE currently has a forward P/E ratio of 14.55, while ECL has a forward P/E of 41.37. We also note that CE has a PEG ratio of 2.47. This figure is similar to the commonly-used P/E ratio, with the PEG ratio also factoring in a company's expected earnings growth rate. ECL currently has a PEG ratio of 3.91.Another notable valuation metric for CE is its P/B ratio of 5.54. Investors use the P/B ratio to look at a stock's market value versus its book value, which is defined as total assets minus total liabilities. By comparison, ECL has a P/B of 10.24.Based on these metrics and many more, CE holds a Value grade of B, while ECL has a Value grade of D.CE sticks out from ECL in both our Zacks Rank and Style Scores models, so value investors will likely feel that CE is the better option right now.Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Celanese Corporation (CE): Free Stock Analysis Report Ecolab Inc. (ECL): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research