The short answer is that no furniture is truly spider- or wasp-proof, but you can make it much less appealing. I’d focus on reducing four things: hiding cracks, damp fabric, hollow nesting tubes, and nearby food or prey. For urban balconies, rooftops, and shared courtyards, that means choosing furniture that is easy to see, clean, and dry out quickly.
Start with smooth, sealed materials. Powder-coated aluminum, stainless steel, resin, and sealed hardwood are better than loose wicker, rattan with deep gaps, or rough unfinished wood. Spiders love quiet corners and crevices, and wasps will use any hollow tube or gap as a nest site. Pick chairs and tables with welded or capped legs, tight joints, and as few underside cavities as possible. Avoid furniture with open-ended tubular frames, built-in planters, or decorative holes unless you can cap or screen them.
Cushions and covers matter, too. Choose removable, quick-drying, washable cushions and store them dry when not in use. A damp cushion left out for days is basically a small insect shelter. Avoid leaving loose covers draped over furniture for long periods; they create dark, sheltered pockets. If you use a cover, make sure the furniture is dry first and the cover fits tightly rather than flapping around.
Keep the setup clean and exposed. Raised legs, open frames, and slatted tops that let water drain are easier to inspect and less likely to collect leaves and webs. Place seating away from eaves, dense shrubs, bins, compost, and flowering plants that wasps visit. Keep food and sugary drinks covered, wipe tables after eating, and use lidded bins. Outdoor lighting near the seating can attract flying insects, which in turn attract spiders, so switch to warmer or yellow bug bulbs and keep lights away from the furniture.
Finally, plan a quick routine. Once a week, wipe smooth surfaces, vacuum or brush out joints, and knock down early webs or small wasp nests. Check undersides and inside armrests, especially in spring. If wasps are already nesting, call a professional rather than disturbing it yourself. The goal isn’t to create a sterile patio; it’s to choose furniture that gives insects fewer places to settle and makes cleaning easy enough that you actually do it.