Folding table and chair sets can be weather-resistant for outdoor use, but it largely depends on the materials and construction of the set. Many outdoor folding furniture sets are specifically designed to withstand various weather conditions, including rain, sun, and wind. 
Materials like powder-coated steel, aluminum, and certain types of treated wood, such as teak or eucalyptus, are commonly used for their durability and resistance to rust and decay. These materials can handle exposure to moisture and sunlight without significant deterioration. Additionally, synthetic materials like high-density polyethylene (HDPE) or resin wicker are popular for their ability to resist fading, cracking, and other weather-related damage.
The design of the furniture also plays a role in its weather resistance. For instance, furniture with slatted surfaces allows water to drain easily, reducing the risk of water damage. Moreover, UV-resistant finishes and coatings can help protect the furniture from sun damage, preventing fading and weakening of the material.
However, not all folding table and chair sets are inherently weather-resistant. Sets made from untreated wood, low-grade metals, or fabrics not designed for outdoor use may not withstand prolonged exposure to the elements. These materials can warp, rust, or degrade over time if left outside without protection.
To ensure longevity, even weather-resistant sets may benefit from regular maintenance, such as cleaning, applying protective coatings, or storing them indoors during extreme weather conditions. Using covers can also provide additional protection against the elements.
In summary, while many folding table and chair sets are designed to be weather-resistant, it's crucial to choose sets made from durable materials and to follow maintenance guidelines to ensure they remain in good condition for outdoor use.