Northern White and Western Red Cedars & Cypress
Both of these woods are native to North America and are traditionally used for boat building, house siding and furniture. They’re valued for their combination of lightweight, interesting grain pattern and extreme durability in outdoor conditions. Although cedar will show knots and cracks in the grain, it maintains its durability for 20 years or more without warping, splitting or rotting. Its light-colored surface will weather to a silver-gray patina. Also, Cedar and Cypress have natural oils that make it bug, mildew and rot resistant.
The king of durable woods, teak will hold up long enough to pass down to the next generation. It needs no maintenance (aside from the occasional light sanding or cleaning to remove surface dirt), is dense and straight-grained, and will not warp or crack over time. Because of its high mineral content, teak resists rotting even in the wettest conditions. Over time, the surface of the wood will weather to a beautiful silver-gray patina. Best treated with Teak Oil.
A renewable resource - eucalyptus is a plantation-grown hardwood that is sustainably harvested and in plentiful supply. This high-quality, kiln-dried timber is incredibly solid with great durability and strength and has beautiful grain and a smooth finish that requires minimal maintenance. Eucalyptus is extremely dense, rot- and decay-resistant with a high oil content that repels water and moisture. It also weathers to a soft gray if left untreated, however, it can be stained to maintain its rich tones.
Native White Oak
Its unique cell structure repels moisture, insects and rot. The famous American sailing ship, Old Iron Side, was built with white oak and could repel British cannon balls. Dense and straight-grained, white oak furniture has an oil finish and can be left to weather to a gray patina or cleaned and re-oiled annually.
This wood looks a lot like ordinary pine, and is similar. That means it’s a softwood that you can easily cut and fasten, just like pine. Douglas fir, though, is more resistant to decay, which makes it much better outdoors. Douglas fir can be sanded very smooth and it takes paint extremely well. You can apply semi-gloss paint (over primer, of course), or even high-gloss to achieve a sleek, smooth look.
NOT SO GOOD WOODS
Chinese Fir - Many "cheaper" furniture is made with this. It comes from China, but it is so far inferior to Douglas Fir. Sure, it is o.k. for outdoor furniture, if you want it to last 2 years (maybe).
Pressure Treated Pine (PT) Pine:
The good: It is easy to buy at the big chain stores or any lumber yard. Not overly expensive, durable for outdoors and long lasting.
The Bad: Chemicals, chemicals, chemicals. I wouldn't recommend licking one. The chemicals can soak into your skin when you sit on it and food can be exposed to them too. That's why they are not used in food preparation such as cutting boards and butcher blocks. Plus, it's a soft wood and easily damaged and splinters, splinters, splinters. One last thing, the sap in pine will ooze out for years. Think of the stains on your shorts or shirt.
Red Oak: Open cell spongy wood that practically drinks water. NO good for outdoor furniture. High maintenance - who wants that?
Well, that's my 2 cents on outdoor furniture wood. Oh, my source is - The World Wide Web.