When looking you will be presented with the choice of how many vents you want in your blazer. A single vent is the most common choice but you can also find blazers with no vents or with double vents. Vents allow for easier movement and greater flexibility; a single vent is the most common and blazers without vents have become very unusual.
Double breasted blazers are the more traditional design and are considerably more formal than their more popular single breasted counterparts. Double and triple button blazers have become more common than single button examples but it is possible to find any combination of these as you require.