Trusted pro quality. Since 1937. 2x thicker (than original formula). Thick, pro strength acidic gel: Clings to inside of bowl. Removes soils, rust, hard water & stains. Pros know that acids are required to dissolve soils, hard water buildup, and rust in toilets. This professional grade acidic formula clings longer to remove stains with less scrubbing, leaving a fresh winter green fragrance. No phosphates.