Spanish cedar is by far the most popular choice. The reason this type of wood is frequently used to line the inside of cases or used for humidor trays is because it is absorbent and helps to stop moisture from building up. This is the most important factor in keeping your cigars fresh and flavorful. Another reason this type of wood is chosen is due to the strong smell. Tobacco worms love to find a tasty cigar to destroy. The strong odor of this wood drives them away. The smell is strong enough to impart a light woody flavor to the stored cigars, a flavor that many people actually enjoy.
Mahogany is the third type of wood you may find used in humidity-battling storage cases. It does a great job of keeping moisture levels down, nearly equal to Spanish cedar. This wood has an extremely mild scent and is preferred by those that do not want a woody flavor imparted to their cigars. The downside of this type of wood is the fact it does not keep tobacco worms away, and any brokenhearted collectors can tell you the damage that tobacco worms can wreak.
Photo via justagirlwithahammer.comWhy is Cedar Used in Humidors? by David Sabot