The shaft can also be made of wood, fibreglass or carbon fibre but another possibility is aluminium, as long as it is a thick-walled extruded tube. The life expectancy of a cheap-and-nasty aluminium shaft (tube welded up from thin sheet metal) is very short. An alloy paddle shaft should have a wall thickness of at least 18 swg. Even a good aluminium shaft is cold and slippery so it needs to be covered with a plastic sheath or some waterproof adhesive tape. 

Wood is an excellent material for paddle shafts and blades. The best Sitka spruce, Western Red Cedar and Douglas fir are springy, light, tough, scarcely affected by fatigue, warm to the touch and naturally buoyant. Blade tips can be made of a dense hardwood or plastic. A wood shaft or blade is usually stronger if it's laminated from multiple layers, sandwiched together with glue, rather than carved from a single piece.

There are plenty of kayakers who would give up chocolate sooner than part with their favourite wooden paddles by Kober, Azzali, Lendal, Mark Gees or Triton. However, wood has to be laminated, sculpted, smoothed and varnished so many manufacturers have dropped it altogether and use only materials that can be shaped in a mould. See Kayarchy Shopping for paddle manufacturers using only composites and those who also use wood. Wooden paddles and plastic composite paddles which are stored for a long period can slowly warp under the influence of gravity, so they're best kept either on a horizontal shelf or hanging vertical.