With a patio conversation set, you face the challenge of selecting a material that will be appropriately durable and waterproof yet completely comfortable. To achieve these goals, you'll need to select two things: A material for the frame of your patio conversation set, and one for the upholstery or cushions.
For the frame, you need a strong material that will neither rust nor rot. Good examples of such materials include stainless steel, treated aluminum, or treated wood (including wicker and rattan). Some heavy-duty plastic versions may also work, but they may be too lightweight and likely to blow away in a heavy gale.
With a rust-proof metal or water-treated wood, you'll be sure to have a durable base that will be able to support you without a second thought. Either can be painted any color of the rainbow and come in numerous styles. Wood may confer a more natural look, whereas metal can give off more industrial vibes.
If your conversation set doesn't have any padding, upholstery, or pillows, then your job is done! However, there's a good chance that you'll have to make a choice for fabric as well. The most common type of fabric used for outdoor furniture is durable duck canvas or treated cotton. Canvas is thicker and will stand up to heavier traffic; cotton comes in more patterns and may be good for decorative pillows. Cotton is also breathable, so it can be an option for those with sensitive skin.
Synthetic materials like polyester or vinyl will do a great job here as they are affordable, easy to clean and durable. Some of them are water-resistant - a great benefit for an outdoor piece of furniture.