A type of resin used to produce plywood which has formaldehyde emissions higher than Phenol and Melamin. It is any of a class of synthetic resins obtained by chemical combination of urea (a solid crystal obtained from ammonia) and formaldehyde (a highly reactive gas obtained from methane). It is less durable than the other two resins and do not have sufficient weather resistance to be used in exterior applications while production costs are lower than the other two resins. Concerns over the release of formaldehyde into the air have led to substitution even here by phenolic.