Plywood is a versatile material that can be used for making indoor as well as outdoor furniture.
For exterior use, as in the case of garden furniture, the plywood that you choose, needs to be completely water-proof so that it can withstand the rains. So for this purpose you need to opt for waterproof exterior grade plywood.
Note that, plywood is available in three different grades in India.
1. MR grade (Moisture Resistant)
This is also known in the market as commercial plywood. It is not waterproof, but simply can resist some amount of moisture. It is suitable for interior use only.
2. BWR grade plywood (Boiling Water Resistant)
This is a waterproof plywood and can be used for meeting your exterior furniture requirements.
As per the quality tests for plywood, that are specified in IS:303 of the Indian Standards organization, such plywood can successfully withstand being submerged in boiling water for a period of 72 hours, without getting damaged.
Plywood is made by sticking and hot-pressing together several layers of wood veneer over each other (called plies), and in the case of such exterior plywood, phenol formaldehyde, which is a synthetic plastic resin is used, which helps to make the plywood waterproof.
Also, the wood used in the manufacturing of such exterior grade plywood is usually sourced from 'hardwood' trees such as 'teak' or 'gurjan', which is much stronger compared to that of 'softwood' trees such as mango wood.
Apart from its use in making outdoor furniture, such plywood is also well-suited for making indoor kitchen cabinets and any other pieces of furniture that are likely to get wet.
3. Marine plywood.
This plywood is of the best quality and is primarily intended to be used for Marine applications (such as in the building of boats, ships, aircraft and in industrial applications). It is very costly, and though it can be used for making exterior furniture, its usually an overkill, because the BWR exterior plywood grade listed above, generally is good enough for this purpose.
In addition to choosing BWR grade waterproof plywood, the second additional thing that would want to do, to increase the durability of your exterior furniture, is to add a topping of laminate (e.g. sunmica) over the plywood.
These decorative laminates are available in a variety of colours, patterns and textures. They not only enhance the beauty of the furniture, but also provide further immunity to it against any water damage, by preventing water from seeping into the wood.