An acid thickener is a substance used to increase the viscosity of acid-based solutions, often for applications that require better adhesion, control, or spreadability. It is commonly utilized in industrial, cleaning, and chemical formulations. 

Acid thickeners are commonly used in acid-based cleaning products, where they improve the cling time and contact effectiveness of the cleaner on surfaces (e.g., in descaling or rust removal).
Cleaning agents for metal surfaces, concrete cleaning, removing mineral deposits, and removing scale from heat exchangers.
Thickeners used in anti-corrosion paints for metals exposed to acidic environments.
Thickeners in acidic beverage formulations (e.g., fruit juices) to maintain consistency.
Acid thickeners are also used in acid-based detergents for household and industrial cleaning tasks, helping to increase the effectiveness and ease of use.