Rayon, in its most simple form, is biodegradable. It is a plant-based material and, as such, will biodegrade in a landfill in around five years. However, that is only true for untreated Rayon. If the fabric has been treated, for instance, to prevent pilling, then it will not biodegrade as quickly. The more processed forms of Rayon can take between 20-200 years to biodegrade.