Plywood is a product that is made from several layers, or veneers of wood. It comes in hardwood and soft wood, and plywood is durable and resistant to warping and cracking that can affect other woods. Glue is the primary bonding agent for plywood, and glue with E0 is known as among the safest glues for plywood because it has the fewest emissions of formaldehyde.
There is a scale of plywood glue that ranges from E0, considered to be the healthiest or safest glue, to E1, which is considered mid-range, up to E2, which has the largest amount of formaldehyde emissions. This scale is used only with glue types that seep formaldehyde, which is a dangerous quality of many plywood glues.
E0 plywood glue is considered to be the safest of the formaldehyde excreting glues. According to Packard Forest Products, E0 glue averages a formaldehyde secretion of under .5 milligrams per liter. That means that there is less than 3 milligrams of formaldehyde secreted per every 100 grams of the glue that is used. This is opposed to E1 which has 9 grams of formaldehyde per 100 grams of glue, and E2 which has 30 grams of formaldehyde for every 100 grams of glue.
In addition to the "E" rating of a glue, there is also a type of glue used in plywood manufacture. Type 1 glue is used in outdoor applications, and it is a phenolic formaldehyde glue. Type 2 glue is used on interior applications, and it is made with a urea formaldehyde combination that works better when kept out of the elements. Either of these types can have a rating of E0 if properly made.
The concern involved in plywood glue is that formaldehyde is carcinogenic, meaning that it is poisonous. Formaldehyde will damage the environment and poison the air and water. It also can be absorbed into the human body, where it will cause harm that ranges from eye and skin irritation to throat irritation, breathing problems, vomiting and, in cases in which formaldehyde is ingested, coma and potential death. Though manufacturers are on the lookout for greener glues, E0 glue has the safest rating with the lowest amount of carcinogen emissions.