Selecting the appropriate combination of scent and substrate is vital for product longevity. For paper-based air fresheners, ensure the use of high-density absorbent cotton paper (usually 1.5mm to 2mm thick) to allow for maximum fragrance retention. When choosing scents, prioritize essential oils or high-quality synthetic fragrances that are IFRA (International Fragrance Association) compliant. Popular scents like 'New Car', 'Lavender', and 'Black Ice' have higher market demand, but you should request SGS or MSDS (Material Safety Data Sheet) reports to ensure the oils are non-toxic and non-allergenic.