There are two kinds of reactive polyurethanes available to the general woodworking market. The first, a reactive polyurethane in hot melt form, is used in a wide range of applications. It is especially suited for assembly projects as well as edge-banding and profile wrapping. The other reactive polyurethane on the market is liquid which works very well in a wide range of applications but, as with all adhesives, there are both positive and negative sides to it. On the positive side, reactive polyurethanes are strong, water resistant and have the ability to bond to a wide range of substrates. On the negative side, they are more expensive that other glue types and are difficult to clean up.