Coated vs uncoated stock; matte / satin / gloss finish
Coated paper seals the surface so ink stays punchy; uncoated soaks it in and goes softer. Matte, satin and gloss set how much it shines.
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What it is
Coated stock has a thin clay or polymer layer sealed onto the sheet, so ink sits on the surface: sharper dots, deeper color, less spread. Uncoated is bare fiber (copy paper, letterhead, the soft natural business card), and it drinks ink in, so colors land duller with softer edges and more dot gain. How much duller depends on the sheet, the ink, and the press, so judge it from a printed sample rather than a percentage someone quoted you. Neither is better. They are different instruments.
Finish is the sheen of the surface you end up with. Sometimes that is the coated sheet itself (gloss art, silk, matte coated), sometimes it is a varnish or laminate applied afterwards, and the same three words get used for both, so say which you mean when you spec it. Gloss bounces light and makes photos pop (catalogs, flyers, packaging), satin or silk is the middle setting that most magazines use, and matte or dull kills glare and is easiest on the eyes for long text. Silk is the safe default when a piece has both photography and body copy.
Gotchas that bite in the real world: gloss and dark matte laminates are fingerprint magnets (a black soft-touch card shows every thumb), and a sealed glossy surface fights most pens: ballpoint smears, gel ink beads up, permanent marker usually bites. That quietly kills gloss for appointment cards and forms unless you leave a writable uncoated panel or ask for a writable coating. If you commit to uncoated, build the artwork for it: push saturation and contrast, drop hairline reversed type, and expect a warm paper white instead of a screen white.
Ask AI for it
Design this piece for uncoated stock and tell me what changes. Assume colors print duller and softer than on screen and that fine detail spreads, then confirm the real amount from a printed sample: raise saturation and contrast, avoid tints below 10%, avoid hairline reversed-out type, and use a warm off-white as the page base rather than pure white. Then give me a coated-silk alternative of the same layout with edge-to-edge photography. For each version, state the stock spec I should send the printer (coating, finish, gsm) and the one practical tradeoff: glare, fingerprints, or whether a pen will write on it.