They are made:
By gluing. This method is quite good for chipalon boats.
Using ultrasonic welding or volcanization. These methods are great for PVC boats.
It is also worth deciding for what purposes you buy an inflatable boat, which capacity is interested in. After its acquisition, do not forget about proper care — it is ideal to store the boat in an inflated state, thereby avoiding the formation of the bends of the material.