Sustainability in composites can be broken down into their production and the way they are handled after use. The materials that make up a composite can be made more sustainable by taking advantage of renewable sources and by using materials whose properties cause less of a lasting impact on the surroundings. Biochar, being one method to incorporate sustainable materials into existing composites, shows promise as a low-cost, biodegradable option for mechanical reinforcement fillers in commodity plastics because it is similarly compatible with materials like polyolefins as other high-carbon fillers are. Cellulose provides a renewable and biodegradable option with possibilities in aqueous environments and hydrophilic materials which can be procured from natural sources through processing plant-matter or from man-made sources with the production of bacterial cellulose. Poly(ε-caprolactone) and Poly (l-lactide) provide examples of plastic materials that can be combined with other existing materials to form biodegradable composites. Recycling, as a daily component of sustainability in materials, is explored through a review of the mechanical recycling method, showing the steps of the process and how each of them fit together. Chemical recycling, as a more modern take on reusing material at the molecular scale, is shown to be a versatile way to use existing materials and create new ones to make a more sustainable cycle. With these methods presented, the importance and processes used in plastic sorting become more important, and the advances in this area shows that smarter technology is keeping up with the push for sustainable practices.