Methods, systems, and apparatus, including medium-encoded computer program products, for reducing or eliminating curl and wrap in additive manufacturing include, in at least one aspect, obtaining a three dimensional (3D) model of a 3D object to be additively manufactured using a thermoplastic material delivery apparatus; generating a variable width brim for at least a first layer of the 3D model, wherein a width of the brim varies from a maximum value to a minimum value at different locations adjacent at least the first layer of the 3D model, and the generating comprises varying the width of the brim in accordance with an amount of convexity of the 3D model in regions corresponding to the different locations; and outputting the variable width brim for use in preventing warping during the additive manufacturing of the object from the 3D model using the thermoplastic material delivery apparatus.