A method of manufacturing a semi-crystalline article from at least one pseudo-amorphous polymer including a poly aryl ether ketone, such as PEKK, including a softening step, wherein the at least one pseudo-amorphous polymer is heated to a temperature above its glass transition temperature to soften the polymer, and a crystallization step, wherein the at least one pseudo-amorphous polymer is heated to a temperature between its glass transition temperature and melting temperature, the pseudo-amorphous polymer being placed on a mold during either the softening step or the crystallization step before at least some crystallization takes place. The method results in articles demonstrating increased opacity, increased crystallinity, increased thermal resistance, improved chemical resistance, and improved mechanical properties over articles formed by traditional thermoforming processes.