When evaluating satin fabric, the fabric weight (GSM - Grams per Square Meter) is critical; for curtains, a weight of 200-350 GSM ensures a luxurious drape. You must also verify the thread count and weave density, as a higher density prevents light leakage and enhances the characteristic 'satin sheen.' Additionally, check for colorfastness to light (Grade 4 or above) to ensure the fabric does not fade under prolonged sun exposure, and confirm the shrinkage rate is controlled within ±3% after washing.