Biopolymers derived from seaweed are promising natural polymers as alternatives to synthetic polymers due to their biodegradability and non-toxicity. These biopolymers can be processed into rigid and strong films, but they need to be blended with other materials due to their limited physical properties. The use of agar has a drawback, as its hydrophilic nature can decrease the properties of bioplastic. Therefore, other materials, such as polylactic acid (PLA) are added to improve the quality of the agar-based bioplastics. The mechanical properties of the bioplastics were evaluated by measuring their tensile strength and elongation. Surface hydrophobicity was determined by measuring the moisture content. Other parameters, such as color and opacity, were also measured. Bioplastics composed of agar/PLA showed tensile strength of 1.21 ± 0.13 to 3.44 ± 0.35 MPa; elongation of 0.96 ± 0.12 to 23.67 ± 0.35%; L* of 47.76 ± 2.68 to 75.80 ± 1.55; a* of 2.20 ± 0.40 to 11.57 ± 0.82; b* of 25.37 ± 1.18 to 44.99 ± 1.47; opacity of 14.86 ± 1.73 to 40.68 ± 3.11; and moisture content of 5.05 ± 0.14 to 9.24 ± 0.22%. The pellets of the agar/glycerol/PLA-bioplastics were processed in an injection molding machine. The products were plates with a production quantity of 5 kg. The injection and cooling time per product was 70 s, and the cleaning time was 50 s. The resulting products have a uniform mass from 144.15 to 144.24 g. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2025.