Please note that some of the facts listed below are of a rather graphic nature. They may be upsetting to pet parents who are currently grieving for a lost loved one. We felt that these facts might be of help to anyone trying to decide between a casket made of wood and a casket made of some other material. These facts are among the reasons Wanda and I chose to make all our caskets from wood.
St. Paul in 1 Corinthians speaks of burial as planting a seed in the earth. We shall rise again and be given a "glorified" body just like a new plant that rises from a seed which is planted. We shall not die, but we shall all be given new bodies when the last trumpet is blown and we will all be together again forever.
If the body has had the misfortune to have been sealed in an airtight metal or plastic casket anaerobic bacteria—that is, those that thrive in an airless environment—will have a chance to get to work, and the body will putrefy, meaning it will partially liquefy. Both plastic and metal are non-biodegradable and could stay in the earth for many thousands of years. Simple wooden caskets, believe it or not, result in more gradual and natural decomposition of the body.
Source: The Straight Dope a registered trademark of Chicago Reader, Inc.
Protective metal or plastic caskets will not stop the decomposition of the body. Instead of the natural dehydration that occurs in a wooden casket taking place, the body that is buried in a permanently sealed metal or plastic casket will putrefy or turn to liquid in the anaerobic bacterial environment.
Source: Caring for the Dead: Your Final Act of Love, by Lisa Carlson, Executive Director of the Funeral Consumer's Alliance
Caskets that are permanently sealed and non-biodegradable such as those made of metal or plastic have been known over time to float out of the ground during rainy seasons where the ground becomes overly saturated with water. This is especially true in the case of "shallow" graves such as those we bury our pets in. This is also true for such caskets that are buried in low lying areas where the natural ground water is near the surface. This problem can be greatly minimized by the use of wooden or other caskets that are bio-degradable and are eventually reclaimed by nature.
Source: Internet Facts
Be aware that there has been some controversy about the use of so called "air-tight" metal or plastic caskets. These caskets are usually much more expensive. The idea is that they keep out water, air, and dirt and preserve the remains. However, reports are that an air-tight casket usually stays sealed for only a short time despite the "many year plus" guarantee. Then, there is the issue of some bodies decomposing and then exploding inside an air-tight casket, the force of the explosion sometimes breaking open a sealed casket. This seldom happens with human caskets on todays market because the air-tight seal is usually designed to allow the gases formed by anaerobic bacteria to escape while keeping out both air and water. Wooden pet caskets, on the other hand, are much less expensive and the seals used are not the same. Take the time to research these facts before deciding if the extra cost is worth it to you. And remember, no casket whether metal, plastic, or wood will preserve a body forever.
Source: Internet Facts