The most common reactive groups are monochlorotriazine (MCT), dichlorotriazine (DCT), and vinyl sulfone (VS), with bifunctional dyes combining two reactive groups for improved fixation. For classification purposes, the specific reactive group chemistry does not change the heading — all covalent-bonding fiber-reactive dyes for cellulosic or protein fibers fall within the reactive dyes heading — but it is commercially critical for specifying fixation conditions and wash-off procedures.

Reactive dyes that hydrolyze during storage or transit lose their ability to bond covalently with fiber, reducing fixation efficiency and increasing wash-off waste at the mill. Importers and buyers typically specify maximum hydrolysis levels and require sealed, moisture-proof packaging with limited shelf life from date of manufacture. Testing on arrival against the supplier's certificate of analysis is standard practice for quality-sensitive buyers.