Rayon is a material made from artificial silk. Artificial silk is created from processed tree materials and pulp from woody plants. Since rayon is made from highly processed plant materials, it is neither entirely natural or entirely synthetic. Rayon is cheap to produce. Polyester is made from processed petroleum. Both products are strong and can be used in a wide variety of materials, from clothing, to bedding, to fabrics used in industry. While these products serve similar purposes and boast similar strengths, they can be distinguished visually and have slightly different benefits and disadvantages.
Rayon and polyester can be distinguished based on the visible luster of the fabric. Rayon features a subtle shine and visually resembles lustrous materials like silk. Meanwhile, polyester has more of an artificial gloss, and as a result, appears shinier. Due to its unnatural level of shine, polyester looks like a clearly artificial fabric, while rayon might be mistaken for a material like silk that is made from natural fibers that have not been heavily processed. In fact, many of the differences between polyester and rayon exist because rayon is made from natural, if highly processed, plant fibers, and polyester is entirely synthetic.
Rayon both appears and feels silkier and softer than polyester. Meanwhile, polyester is a slightly harder fabric that appears stiffer than rayon.
Rayon drapes better than polyester. If a fabric appears to be especially pliable and hangs in small pleats when draped, it is most likely rayon. If it appears to be slightly stiff when draped, it is most likely polyester. Polyester keeps its shape better than rayon, so a garment or piece of bedding that appears to be slightly rigid is probably made from polyester. This fabric is visibly stronger and more durable than rayon.
You can sometimes distinguish between rayon and polyester by sight, based on the way that fabric is being used. Rayon can be easily dyed, so fabrics of vibrant colors are likely rayon. Rayon can also withstand higher temperatures than polyester, so if you see fabric being used in high-heat situations, such as at factories where plastics or other materials are melted and molded, the material in use is most likely rayon. Polyester, meanwhile, dries quickly and is water-resistant, so outdoor clothing made to withstand extreme conditions is probably made from polyester fabric. Polyester is also insulating and easy to wash and dry and is therefore often used to make hiking and backpacking equipment such as tents and sleeping bags.