Based on their application method, flame retardants can be classified into additive types and reactive types. Additive flame retardants are typically incorporated into the base resin through simple physical mixing. In contrast, reactive flame retardants are monomers containing both flame-retardant elements and reactive groups-such as halogenated anhydrides, halogenated bisphenols, and phosphorus-containing polyols; due to their reactivity, they can chemically bond to the resin's molecular chains, becoming an integral part of the plastic resin itself (notably, the structures of many reactive flame retardants also serve as monomers for synthesizing additive flame retardants).

Flame retardants can also be categorized by chemical composition into inorganic and organic types. Inorganic flame retardants include aluminum hydroxide, magnesium hydroxide, antimony oxide, zinc borate, and red phosphorus. Organic flame retardants primarily consist of halogenated hydrocarbons, organic bromides, organic chlorides, phosphate esters, halogenated phosphate esters, nitrogen-based flame retardants, and nitrogen-phosphorus intumescent flame retardants. Smoke suppressants-often molybdenum, tin, or iron compounds-serve to reduce smoke generation and the release of toxic or harmful gases from flame-retardant materials. Although antimony oxide and zinc borate possess smoke-suppressing properties, they are frequently used as flame-retardant synergists and are thus classified within flame-retardant systems. Flame retardancy is a critical performance requirement for the vast majority of plastics; traditional flame-retardant materials rely on halogen-containing flame retardants. However, halogenated materials generate significant amounts of smoke and toxic, corrosive gases during combustion, leading to secondary hazards. Common flame-retardant formulations include phosphorus-based compounds, silicon-based flame retardants, nitrogen-based flame retardants, and metal hydroxides; these are known as environmentally friendly flame retardants because they do not volatilize or produce corrosive gases during combustion.