What is the difference between baking paper, greaseproof paper and foil?
Three different materials with different properties, routinely substituted for each other with unpredictable results.
Baking parchment (baking paper). Paper treated with silicone, giving a genuinely non-stick surface that is heat resistant to high oven temperatures. This is the one for lining tins and trays — nothing sticks, it can usually be reused, and it handles direct oven heat well.
It is the correct choice for biscuits, cakes, roasting vegetables and anything likely to stick.
Greaseproof paper. Paper made dense by mechanical treatment so fat cannot pass through, but not silicone coated. It resists grease; it is not non-stick, and it needs greasing to behave like parchment.
It is also less heat tolerant. Suitable for wrapping, for layering between items, and for lining tins if greased — but it will stick if used bare, which is the usual disappointment.
Aluminium foil. Metal. Conducts heat, which is the fundamental difference — parchment insulates slightly, foil transmits. This means foil browns the surface it touches more, and can cause the base of a cake or the bottom of a biscuit to over-brown.
Not non-stick, so acidic or sugary food adheres and tears. It also reacts with acidic foods such as tomato, citrus and vinegar over long contact, which can pit the foil and leave a metallic taste.
Excellent for covering to prevent over-browning, for parcels, for wrapping resting meat, and for lining trays where the tray needs protecting rather than the food.
Never in a microwave.
Which to use:
Lining a cake tin or baking tray — parchment.
Covering something to stop it browning — foil, tented rather than pressed on.
Roasting where you want browning underneath — nothing, or foil.
Wrapping food for storage — greaseproof or foil, depending on whether it is acidic.
En papillote (cooking in a sealed parcel) — parchment, which allows some steam expansion.
Silicone mats are the reusable alternative to parchment, excellent for biscuits and less good where you want a crisp base, since they insulate.