When evaluating a sofa set, the internal structure is as critical as the exterior. You should prioritize kiln-dried solid wood frames (such as larch or oak) to prevent warping and cracking. For cushioning, ensure the high-density foam has a rating of at least 35kg/m³ to prevent sagging over time. If sourcing leather, verify if it is Top Grain Leather or split leather, as this significantly impacts durability and price. For fabric options, check the Martindale rub count; a rating of 20,000+ is essential for residential use, while 50,000+ is required for commercial/contract environments.