Thestral tail hair

A Thestral tail hair is a hair taken from the tail of an unusual creature known as a Thestral, and has been used in the cores of wands. It is regarded as an unstable, if not difficult substance to use in wand making, though Veela Hair is also described as such, but has been successfully utilised.

A Thestral

Known Wands

The Elder Wand, only known core user of Thestral Hairs.

The only known wand to have used a Thestral Tail hair is the legendary Elder Wand, alternately known as "The Deathstick" and "Wand of Destiny" and many others. The Elder Wand, created either by Death or Antioch Peverell, is recorded to be the most powerful wand in the world, and by legend was made by Death to make the user invincible in wizard duelling.

Whether this is a testament to the power of the Thestral tail hair remains ambiguous, as Elder Wand bearers have been shown to be defeatable in a duel (Gellert Grindelwald for example). Nevertheless, the Elder Wand has shown additional powers that other wands are not capable of, such as being able to successfully repair other wands, which was thought to be impossible.

The tail hair in the Elder Wand being overpowered because the Wand wood broke with the Shield penetration spell

It is assumed that one must be able to see Thestrals in order to utilise their hair, and since one must witness death first-hand to see a Thestral, anyone wishing to forge a wand with the hair must witness death, tying in with the story of being "Master of Death." It also seems that if the wand has been slightly cracked, and the true master of the wand casts a spell, and the person possessing the elder wand casts a spells, the true master's spell will push both spells through the cracks in the wand, killing the possessor of the elder wand and disarming them. It is unknown if the tail hair would be visible to a wandmaker who had not seen death, as a Thestral would be, or if it can be scene once its seperated from the thestral.