When evaluating 100ml HDPE (High-Density Polyethylene) bottles, you must focus on material density and wall thickness to ensure chemical resistance and structural integrity. Look for a gram weight of at least 10g-12g for a standard 100ml bottle to prevent collapsing during filling. Ensure the neck finish (e.g., 20/410 or 24/410) is compatible with your intended closures, such as flip-tops, fine mist sprayers, or lotion pumps. Additionally, verify the opacity levels if your product is light-sensitive.