The neck is made from Cedrella (Spanish Cedar) and is reinforced with ebony, either inlaid below the fretboard, or as a through splice.
The shape of the neck has an effect on playability. Some players like a chunky, D-shaped cross section, others prefer a thinner, elliptical profile.

The necks on my guitars have a fairly slim C-profile, and can be customised to suit personal preference on commissioned instruments.