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Using the well known "displace, cut and reflect" method used to generate disks from given solutions of Einstein field equations, we construct some relativistic models of time dependent thin disks of infinite extension made of a perfect fluid based on the Robertson-Walker metric. Two simple families of models of disks based on Robertson-Walker solutions admitting Matter and Ricci collineations are presented. We obtain disks that are in agreement with all the energy conditions. Key words: general relativity; thin disks; exact solutions; robertsonwalker metric. Highlights• We construct time dependent disks of infinite extension made of a perfect fluid based on the well known Robertson-Walker metric.• The models are interpreted as a disk-like matter distribution made of a perfect fluid with negative pressure or tension immersed in a Robertson-Walker type cosmological model.• The solutions satisfy all the energy conditions. 1 PhD. en Ciencias Naturales, ggarcia@utp.edu.co, Universidad Tecnológica de Pereira, Pereira, Colombia. PhD. en Tecnología Eléctrica, materiales, generación y distribución, egarcia@udea.edu.co, Universidad de Antioquía, Medellín, Colombia. Universidad EAFIT 131|Relativistic models of thin disks immersed in a Robertson-Walker type spacetime Modelos relativistas de discos delgados inmersos en un espacio-tiempo tipo Robertson-WalkerResumen Usando el método de "desplazamiento, corte y reflexión" se construyen algunos modelos relativistas exactas de soluciones que representan discos delgados de extensión infinita, dependientes del tiempo y hechos de un fluido perfecto, basados en la métrica de Robertson-Walker. Se presentan dos familias simples de modelos de discos basados sobre el espacio tiempo de Robertson-Walker que admiten colineaciones de Ricci y de materia. Se obtienen modelos de discos que satisfacen todas las condiciones de energía.Palabras clave: relatividad general; discos delgados; soluciones exactas; métrica de robertson-walker.