Aluminum chloride is the most commonly used mummifying agent in gingival retraction cords because it effectively causes hemosasis and mild astringency without significant tissue irritation. It works by precipitating proteins, leading to gentle hemostasis and shrinkage of the gingival tissues, which facilitates clear impressions. Compared to other agents like ferric sulfate, aluminum chloride is less acidic and causes minimal post-operative tissue inflammation, making it safer for delicate gingival tissues during dental procedures. Its compatibility with impression materials also enhances clinical outcomes.

Reference: Principles and Practice of Operative Dentistry, Satheesh Kumar, 4th Edition.