This Spanish cedar neck blank is reinforced with a graphite-epoxy rod (the black strip in the middle) which is extremely stiff and at the same time light weight.  An unreinforced neck like the ones used on most classical guitars will eventually develop excessive forward bow from the stress of the strings, even if the fingerboard was straight when the guitar was made.  Some builders use other reinforcements, typically hardwoods like rosewood or ebony, but the effectiveness  of these reinforcements is limited at best.

This neck will be so stiff that the fingerboard will need a little bit of forward bow trued in before the frets are installed in order to minimize adjacent-fret string buzzing in the completed guitar.