**1. Introduction**

Flame retardant and thermally insulative polymers are of technological importance and fundamental interest [1, 2]. Polymers continue to infiltrate modern technologies such as aviation, automotive industry, building construction, electronics, to name a few, thanks to their unique combination of properties not available from any other known materials [3]. Polymers are lightweight, durable, easy to process, electrically insulative and corrosion resistant [4]. Common polymers are also thermally insulative [5]. However, polymers are combustible because of their chemical structures that are made up by carbon and hydrogen atoms [6–8]. To meet flammability standards, flame retardants for fireproof polymers have been developed [9, 10].

To protect human life and property, flame retardant polymers are generally made by adding flame retardants into polymers [11, 12]. There are drawbacks in common halogenated flame retardants, which associate with the release of toxic or corrosive by-products [13–18]. There are environment and health concerns caused by these released toxic gases [19]. Therefore, developing highperformance, non-toxic, low-cost, and environmentally friendly flame retardants are needed [19, 20]. Understanding mechanisms for fire retardancy is essential for developing new effective flame retardants. Improving fire retardant behaviors of polymers play key roles in future industrial applications such as furnishings, transportation products and building construction materials [9, 21–25].

Over the past decades, different flame retardants for polymers have been developed [20]. Mechanisms of polymer flame retardancy have been further investigated [9, 20, 26, 27]. Flame retardants have been generally broken into categories based on chemical compositions, which are grouped based on whether they contain bromine, chlorine, phosphorus, nitrogen, boron, or inorganic fillers (metals, etc.) [28]. It is widely recognized that all categories of flame retardants act either in vapor phase or condensed phase to inhibit or to stop combustion processes through a chemical and/ or physical mechanism [29]. Flame retardants can interfere with combustion during a particular stage, e.g., during heating, pyrolysis, ignition, or flame spread [9, 20, 27, 30]. Flame retardants can either act chemically (reaction in the condensed or gas phase) and/or physically (by cooling, formation of a protective layer or fuel dilution) [17]. The polymer flammability properties have been investigated by their ignitability, flame spread and heat release characterizations [20]. Depending on the targeted application of polymers, one or more of specific flammability criteria (e.g. ASTM's fire and flammability standards) need to be satisfied [31].

In addition to flame retardancy, thermal insulation property of polymers can be another significant function that can defend targets against heat damage and save lives [32–35]. Fully understanding the flame retardance and thermal insulation mechanisms in polymers remain challenging. Advanced polymers with combined properties of flame retardancy, mechanical strength and heat insulation are needed. Such polymers will provide broader prospect in civil applications than singlefunction polymers, for example, building insulation applications [36–38].

This introductory chapter not only aims to present the current landscape flame retardant and thermally insulative polymers, but also highlights next generation of flame retardant and thermally insulative polymers for fire protections applications. This introductory chapter summarize fundamental interests and technological importance of flame retardant and thermally insulative polymers, which include principles of polymer flammability, theory of flame retardance, thermally insulative and fire-retardant polymers, and critical discussion and outlook.
