Wand Core

The core of a wand is a magical substance placed within inside the length of wood. They are usually bits extracted from some sort of Magical Being or Creature. The materials used for wand cores can vary widely, though certain wand-makers may prefer to use certain materials; for example, Garrick Ollivander discovered and pioneered the use of phoenix feathers, dragon heartstrings, and unicorn tail hairs, wheras his father used lesser substances such as Kelpie hair and Kneazle whisker.

Some information compiled from Harry Potter Wiki's Wand Core pages among other sources.

Supreme Cores

Ollivander uses ONLY these three cores. Though other wandmakers use these cores in their wands as well.

Phoenix Feather

This is one of the rarest core types. Phoenix feathers are capable of the greatest range of magic, though they may take longer than either unicorn or dragon cores to reveal this. They show the most initiative, sometimes acting of their own accord, a quality that many witches and wizards dislike.

Phoenix feather wands are always the pickiest when it comes to potential owners, for the creature from which they are taken is one of the most independent and detached in the world. These wands are the hardest to tame and to personalise, and their allegiance is usually hard won.

Dragon Heartstring

As a rule, dragon heartstrings produce wands with the most power, and which are capable of the most flamboyant spells. Dragon wands tend to learn quicker than other types. While they can change allegiance if won from their original master, they always bond strongly with the current owner.

The dragon wand tends to be easiest to turn to the Dark Arts, though it will not incline that way of its own accord. It is also the most prone of the three cores to accidents, being somewhat temperamental. It also tends to be lethally hazardous if combined with certain woods, such as Cherry or Yew.

Unicorn Tail Hair

Unicorn hair generally produces the most consistent magic, and is least subject to fluctuations and blockages. Wands with unicorn cores are generally the most difficult to turn to the Dark Arts. They are the most faithful of all wands, and usually remain strongly attached to their first owner, irrespective of whether he or she was an accomplished witch or wizard.

Minor disadvantages of unicorn hair are that they do not make the most powerful wands (although the wand wood may compensate) and that they are prone to melancholy if seriously mishandled, meaning that the hair may ‘die’ and need replacing.

Other Cores

Less Common, but some wandmakers still use them.

Demiguise Hair

Transfiguration

Hippogriff Talon

Charms

Runespoor Fang

Dark Magic

Kelpie Mane Hair

Good for all types of Wandwork, common core in the past.

Ashwinder Ash

Protection Charms

Kneazle Whisker

Not very powerful.

Moon Cicada Wing

Often matched with witches. Helpful for nature magic. Not especially explosive. Natalie Morrow has a wand of this core.

White River Monster Spine

Produces spells of force and elegance. Few wandmakers specialise in luring these creatures so as to sustain the population, so wands with these cores tend to be few in number.

Specialty Cores

Very Rare, often passed down through a family.

Chimera Scale

Rare and extremely Powerful.

Leprechaun Hair

Temperamental to the Non-Irish. Luck and Money charms.

Veela Hair

Extremely temperamental, volatile to non-Veelas. Transfiguration.

Fairy Hair

Good for charms, especially love and beauty charms

Thestral Tail Hair

Extremely rare, only one wand (the Elder Wand) rumored to have a thestral hair core.

Lion Turtle Shell

Rare in the UK, but it used to be popular in the Pacific Islands. With Lion Turtles as an endangered species, newer wands are not made with this core. It is good for elemental magic, but weak in dark arts. It is best paired with someone who has honorable intentions.

Notes

The core type is known to influence the "personality" of the wand produced with it. For example, the wand-maker Garrick Ollivander will not use Veela hair for cores because he believes they make for "temperamental" wands. Another interesting feature of wands and their cores is that if two wands have cores from the same source — such as the same phoenix or unicorn — they are said to be brothers. This can induce Priori Incantatem if the wands come into conflict with one another, such as casting different spells towards each other at roughly the same time.

Prior to Ollivander's practice of using only the three "Supreme Cores", it was common for witches and wizards to present a wandmaker with a magical substance to which they had a particular attachment for use as a wand core. Such substances may have included Veela hair, Kneazle whiskers, Dittany stalks, or Kelpie manes.