A press apparatus and method for steam pressing a mat of compressible material and a binder into a formed product and has particular application to the steam pressing of lignocellulosic material and a binder to form composite board and includes a border projection means generally configured to the outline of the end product to be produced and which is carried by a press platen, preferably the upper press platen, and which is intended to impinge into the mat during its compression and to effect a steam pressure seal at the impingement area of the mat. As a pressure seal of the compressed mat is created about the mat edges, steam can then be passed through the mat in order to cure the binder. If desired, cool air can be passed through the mat afer steaming to condense residual steam in the mat. The compressed mat after steaming, can also be subject to vacuum prior to releasing it from the press. The edges of the cured mat which have been subject to impingement, can subsequently be trimmed off.