Dry weather or environments can cause irreparable damage to acoustic guitars, in the form of fine cracks in the wood.

One way to supply additional humidity to your guitar is through a device known as a guitar humidifier. These devices are designed to release humidity inside the guitar through the sound-hole. Sound-hole humidifiers all utilize some type of water reservoir with an absorbent medium such as a sponge, water absorbent floral foam or absorbent polymer. The medium is then surrounded by some type of cover which holds the water absorbent medium in place and restricts the flow of water evaporation from the medium. To get inside your guitar, they slip between your guitar strings and are held in place there. Depending upon the brand of humidifier you purchase, it may or may not touch the wood inside your guitar. Dampit is designed to lie inside your guitar, while Planet Waves and Oasis are completely suspended from the strings.

Water holding capacity and the restrictiveness of the outer cover are the greatest factors in determining how often you will need to refill the device. Needless to say, you can’t stick a quart container of water inside your guitar, but there are several humidifiers that will hold an ounce (30 cc’s) or more such as Oasis or Planet Waves. If your guitar needs several cc’s per day of water vapor, a humidifier that holds only 5-10 cc’s will need to be refilled every few days.

Planet Waves and Dampit utilize holes in the outside membrane to release water vapor. Oasis uses a fabric which allows the water vapor, but not the water, to pass through the material to keep your guitar humidified. One downside to evaporation holes is the risk of water leakage. Very careful handling can minimize, but not eliminate this risk. Oasis is a water-tight, sealed unit which eliminates the risk of water leakage.

When to refill your humidifier is one of the great mysteries which have been solved by Oasis. Since Oasis is a flexible sealed container, is shrinks as the water inside of it evaporates through the fabric. When Oasis begins to look like a prune, you need to refill it.

All of the sound-hole humidifiers work. Each has its own advantages and disadvantages. As with any new product you purchase, please read the directions carefully before use product you purchase.