A simple method for determining the presence of cadmium (Cd) in thermoformed and biodegradable flexible films and flour and starch samples from cassava, using graphite furnace-atomic absorption spectrometry (GF-AAS), is proposed. The biopolymers used in contact with foods can contain Cd due to contamination from the origin of the material used to make them. The nitric: perchloric acid digestion with reflux was optimized, and the statistical quality parameters were standardized. The GF-AAS instrumental conditions and the graphite furnace heating program were adjusted through pyrolysis and atomization curves, and the optimal temperatures were 530 and 1750°C, respectively. In addition, under optimal conditions, the working range was from 0.1 µg/L to 1.0 µg/L, with limits of detection and quantification of 0.02 and 0.07 µg/L, respectively. The precision was evaluated using intermediate precision and repeatability of the method, which showed standard deviations of 1.6–4.8% and 2.1–4.8%, respectively. The percentage of recovery of Cd ranged from 96.2% to 97.3%. The results obtained support the suitability of the method for determining the presence of Cd in these samples. Cd concentrations in flexible films and starch were below the quantification limit. The other samples (thermoformed and flours) contained less than 1 mg/kg (maximum level set by the NTC 4096), indicating that these polymers meet this standard and therefore can be used for food containers and packaging for fresh fruits and vegetables.