The increasing use of high-strength steels in construction has raised the importance of high-strength filler materials. There-fore, precise control of the mechanical properties of these fillers is crucial, as their strength often closely matches that of thebase material. Heat input during welding can weaken slightly overmatched joints, turning them undermatched and compro-mising the safety of the welded component. In this context, the ongoing AiF-FOSTA research project P1453 investigatesthe impact of cooling time t8/5 on the mechanical properties of weld metals in gas-shielded metal arc welding. Furthermore,the introduction of the new Eurocode 3 Part 1–8 allows the consideration of the nominal tensile strength of the filler mate-rial for fillet and butt welds, directly affecting the design resistance of the welded joint and increasing the importance of thefiller material’s tensile strength. Experimental characterizations of filler materials G62 and G89 on new centric drilled flattensile specimens highlight the correlation between tensile strength and cooling time. The study reveals that the standardizedtensile strength requirements for filler materials of strength classes G79 were not reliably met for cooling times of 7.5 s andbeyond. Moreover, the study indicates that the filler material E89 consistently fails to meet the specified minimum tensilestrength requirements by 5%. However, filler materials such as G35, G42, G62, and G69 consistently comply with normativestandards. These results emphasize the critical need to consider welding parameters, particularly cooling time, to ensureweld quality and structural integrity.