Citation: Malet-Damour, B.; Habas, J.-P.; Bigot, D. Is Loose-Fill Plastic Waste an Opportunity for Thermal Insulation in Cold and Humid Tropical Climates? Sustainability 2023, 15, 9483. https://doi.org/10.3390/ su15129483 Academic Editor: Mohammad Peydayesh Received: 16 May 2023 Revised: 9 June 2023 Accepted: 10 June 2023 Published: 13 June 2023 Copyright: © 2023 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/). sustainability Article Is Loose-Fill Plastic Waste an Opportunity for Thermal Insulation in Cold and Humid Tropical Climates? Bruno Malet-Damour 1, * ,† , Jean-Pierre Habas 2 and Dimitri Bigot 1 1 PIMENT Laboratory, University of Reunion Island, 97430 Le Tampon, France; dimitri.bigot@univ-reunion.fr 2 ICGM, CNRS, ENSCM, University Montpellier, 34293 Montpellier, France; jean-pierre.habas@umontpellier.fr * Correspondence: bruno.malet-damour@univ-reunion.fr † Current address: 120 Avenue Raymond Barre, 97430 Le Tampon, France. Abstract: This paper addresses the plastic waste management challenge by proposing a sustainable solution for the building sector. The proposed solution uses Loose-Fill Plastic Waste (LFPW) as a thermal insulation material, the world’s first in plastic waste recovery. To investigate the potential of this new path, an experimental study was conducted on test cells in Reunion Island’s cold and wet climate. It was revealed that LFPW (size between 3 and 4 mm with 8 cm thickness) can reduce surface temperatures by nearly 3.2 °C, with a maximum difference by almost 22.2 °C. The thermal phase shift is significant (190 mn) and comparable to conventional thermal insulation solutions. The study results suggest that LFPW can provide an effective and economical solution to the challenge of plastic waste management while promoting sustainable development. Keywords: recycling; tropical buildings; experimentation; plastic waste; thermal insulation; loose-fill 1. Introduction Waste management, especially plastic waste, is becoming an increasingly pressing issue. Global waste production is expected to increase by nearly 70% by 2050, with plastics being a major contributor to this problem [1]. Despite plastics’ low cost and versatility, their long-term stability creates contamination problems, especially in emerging countries where waste disposal is not adequately controlled. The Sustainable Development Goals (SDGs) were established to address this issue, with “Responsible Consumption and Production” identifying solid waste recycling as a top environmental challenge. Although developed countries are making progress, emerging countries need to do more to tackle the problem. One potential solution is to shift from “waste management” to “resource management”. Several authors have studied the environmental impact of using recycled plastic in building materials. A 2011 study found that using recycled plastic reduced the carbon footprint of insulation boards by 50% [2], while a 2014 study suggested that recycling PET would decrease its negative impacts [3]. Plastic waste has potential and can be used in construction in different ways. One method is to integrate plastic waste as aggregates in composite concrete or mortar, which can improve its resistance to cracking and increase lifespan. However, plastic–cement interactions are weaker than those observed in natural aggregates, and an increase in the proportion of plastic leads to a reduction in mechanical stiffness. Another method is adding plastic fibers to cemented composite materials, improv- ing their mechanical properties. The reduced fiber required in the formulation makes it a low-waste plastic solution. Indeed, the optimum volume fraction is about 1%. Beyond this, the mechanical properties are weakened, and many articles demonstrate this [4–7], while thermal properties can be improved [8,9]. One method to produce composite concrete involves converting solid plastic into a polymer resin as a binder, mixed with aggregates and sometimes additives. This process is similar to traditional concrete methods, involving vibration, hardening, and molding. Various studies have described techniques for produc- ing liquid resin from plastic waste [10–12]. This method can only handle a maximum of Sustainability 2023, 15, 9483. https://doi.org/10.3390/su15129483 https://www.mdpi.com/journal/sustainability