Citation: Mohd Sabee, M.M.S.; Itam, Z.; Beddu, S.; Zahari, N.M.; Mohd Kamal, N.L.; Mohamad, D.; Zulkepli, N.A.; Shafiq, M.D.; Abdul Hamid, Z.A. Flame Retardant Coatings: Additives, Binders, and Fillers. Polymers 2022, 14, 2911. https:// doi.org/10.3390/polym14142911 Academic Editor: Ilker S. Bayer Received: 16 June 2022 Accepted: 1 July 2022 Published: 17 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Review Flame Retardant Coatings: Additives, Binders, and Fillers Mohd Meer Saddiq Mohd Sabee 1 , Zarina Itam 2, *, Salmia Beddu 2 , Nazirul Mubin Zahari 2 , Nur Liyana Mohd Kamal 2 , Daud Mohamad 2 , Norzeity Amalin Zulkepli 1 , Mohamad Danial Shafiq 1 and Zuratul Ain Abdul Hamid 1, * 1 Emerging Polymer Group, School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Engineering Campus, Nibong Tebal 14300, Pulau Pinang, Malaysia; meersaddiq@gmail.com (M.M.S.M.S.); zeityzulkepli@gmail.com (N.A.Z.); danialshafiq@usm.my (M.D.S.) 2 Department of Civil Engineering, College of Engineering, Universiti Tenaga Nasional, Kajang 43000, Selangor, Malaysia; salmia@uniten.edu.my (S.B.); nazirul@uniten.edu.my (N.M.Z.); yana_kamal@uniten.edu.my (N.L.M.K.); daud@uniten.edu.my (D.M.) * Correspondence: izarina@uniten.edu.my (Z.I.); srzuratulain@usm.my (Z.A.A.H.) Abstract: This review provides an intensive overview of flame retardant coating systems. The occurrence of flame due to thermal degradation of the polymer substrate as a result of overheating is one of the major concerns. Hence, coating is the best solution to this problem as it prevents the substrate from igniting the flame. In this review, the descriptions of several classifications of coating and their relation to thermal degradation and flammability were discussed. The details of flame retardants and flame retardant coatings in terms of principles, types, mechanisms, and properties were explained as well. This overview imparted the importance of intumescent flame retardant coatings in preventing the spread of flame via the formation of a multicellular charred layer. Thus, the intended intumescence can reduce the risk of flame from inherently flammable materials used to maintain a high standard of living. Keywords: additive; binder; coating; filler; flame retardant; intumescence 1. Introduction Coating is a layer of a material or substance in the form of liquid, gas, or solid that is applied onto the surface of an object, which is commonly referred as substrate [1]. Basically, coating may be applied for different purposes, such as decorative, functional, or both [2]. For instance, paints and lacquers are coatings that have the dual purpose of protecting the substrate and being decorative. Artists may use paints only for decoration, whereas the paints on large industrial pipes are used for function: corrosion prevention and identification (i.e., blue for process water, red for firefighting control) [2]. Other than that, functional coatings can be used to modify the surface properties of a substrate, such as adhesion, wettability, corrosion resistance or wear resistance, and surface roughness [3]. In semiconductor device fabrication, which uses a wafer substrate, the coating is applied to introduce completely new properties and functionalities without affecting the bulk substrate, such as magnetic response or electrical conductivity, and becomes an essential component of the final product [4,5]. In fact, a major consideration for most coating processes is that the coating must be applied at a controlled thickness. Various processes are used to achieve this control, ranging from a simple brush for painting a wall to very expensive machinery used in the electronics industry [6]. Another consideration is ‘non-all-over’ coatings in which control over where the coating is applied is required. Printing is one of the examples of non-all-over coating processes in which only a specific area on the substrate is coated [7]. Apart from that, a thin film of functional material is applied to a substrate, such as paper, fabric, foil, or sheet stock, in many industrial coating processes. If the substrate begins and ends the process Polymers 2022, 14, 2911. https://doi.org/10.3390/polym14142911 https://www.mdpi.com/journal/polymers