Recycled-plastic panels are increasingly proposed for noise barriers, but certifying their airborne sound insulation (EN 1793-2) requires full-size specimens and accredited facilities. This communication proposes a screening step for use before certification. It combines the field-incidence mass law with a coincidence correction, Monte Carlo propagation of the unmeasured stiffness and damping, the EN 1793-2 single-number rating DL_R over 100–5000 Hz, and a decision rule: proceed to certification if the 5th percentile of DL_R is at least 25 dB. The in situ rating DL_SI is then estimated from published DL_SI–DL_R correlations. The method reproduced the laboratory R_w of six commercial polycarbonate and poly(methyl methacrylate) barrier sheets within −2 to +3 dB, and the certified DL_R of seven products within −1.8 to +1.3 dB (root-mean-square error 0.9 dB), with no false passes when the threshold was varied from 24 to 34 dB; random- and normal-incidence models were biased by −3.1 and +5.8 dB. Applied to 25 mm panels extruded from unsorted, unwashed mixed plastic waste, it gave a median DL_R of 33 dB and a 5th percentile of 32 dB (29–34 dB for ribbed panels), so the material warrants certification. As the validation covers solid polymer sheets only, testing must confirm the prediction for the recycled material.