Properties at work: why products are made from the materials they are

A non-stick frying pan is metal underneath. But the dark coating that your eggs slide around on is not metal at all. So what is it? A special metal, or some kind of glass, are the usual guesses, and both are wrong. The coating is a polymer, and it was found by accident in nineteen thirty-eight. A chemist called Roy Plunkett opened a cylinder that should have held gas, and found the inside coated with a slippery, waxy white solid. Why would a cook want that one material on a pan, and not just any plastic? We will name that coating and see why it suits a pan, once the properties are sorted.

When a question asks what a product is made from, a group word like plastic, wood or metal is not an answer. The answer is the specific material, because its own properties decide what it can do. Try that on two everyday things. Flick open the lid on a shampoo bottle: the thin strip joining lid to bottle bends thousands of times and never cracks. Now bend a hard, clear plastic ruler that sharply, just once, and it snaps in two. Both get called plastic. So why does one survive and the other fail? Because plastic is a group, not a material. The hinge is polypropylene, PP for short, tough and flexible enough to fold over and over. The other is acrylic, which is stiff but brittle. If your own one flexes instead, it is a different polymer, which proves the same point. One examiner's report gives that advice in so many words. Candidates should be advised against giving generic names of materials, such as plastic, or generic reasons, such as easy to work with, as these are not awarded marks. The fix is to name the material every time, in full the first time, then its short name: polypropylene, then PP. A property does two jobs in an answer. It influences use, which means it decides which products the material can be used for. And it affects performance, which means how well the product then works, in use and over time. PP's flexibility influences its use, because it is why PP can be made into a one-piece hinged lid. It affects performance too, because that hinge lasts as long as the bottle and needs no separate pin. Now sort this line. Because PP resists the chemicals in shampoo, the lid does not swell or weaken in a wet shower. Is that line about influencing use, or about affecting performance? Affecting performance. It says how well the lid keeps working, wash after wash, over the life of the bottle.

One way a question asks all this: choose a material, then answer in three steps. Name one property of it, give a product that uses it, then describe why it is used in that product. Here are five specific materials: beech, stainless steel, polypropylene, duplex board and wool. Take polypropylene. The property: polypropylene is tough and flexible, so it can bend again and again without cracking. The product: the flip-top lid on a shampoo bottle. For the last step, describing why, a student writes this: it is used because it is flexible. What does that last answer add that the property step had not? Nothing new. It repeats the property word. The describing step has to say what the property does in this product. A better describing step adds a layer. The lid is joined to the bottle by a thin strip of PP that folds every time it opens. Because PP can flex thousands of times without cracking, the hinge lasts as long as the bottle. And because PP resists moisture and the chemicals in shampoo, it does not swell or weaken in a wet shower. A second property, used well, adds a second layer. Two words never work as the property. Cheap is a price, not a property, and strong only counts when it names the force it resists. One examiner's report on a question shaped like this records both sides of it. Most students were able to give one product using their identified chosen material. Popular responses were furniture for oak and drinks can for aluminium. Several responses, however, were very superficial in their content and so failed to access all available marks. For example, stating a material was strong, cheap, or soft without further qualification did not score marks. Both lines are true. Naming a product was the step most students managed, and the describing step was where bare words fell short. So the habit is to make the describing step say what the property does, in this product.

Your course asks you to answer this for at least one material area of your choice. That is why each area now gets one strong example, and the one for your own area is the one to master. If you are doing timbers, the beech example is yours. If not, it will not hurt to know, but it is not must-know, and the same goes for every other area. Papers and boards: duplex board folds cleanly and has a smooth white side that prints well, so a cereal box folds into shape and carries a sharp picture. Timbers: beech is hard and tough, so a kitchen spatula resists dents from the edges of pans. Metals: stainless steel resists rust and staining, so cutlery stays bright through years in the dishwasher. Polymers: polypropylene, the hinged lid. Textiles: wool traps air and insulates, so a winter hat keeps your head warm. Now beech in more depth. A set of children's building blocks is made from beech, and a question wants the working properties of beech that suit them. Smooth, hard, rounded corners, tough: which two are working properties of beech? Hard and tough. Smooth and rounded corners are features of the finished blocks, put there by the maker, not properties of the timber itself. Each one then becomes a linked answer. Beech is hard, so blocks that are dropped and knocked together keep flat faces and still stack. It is tough, so a block thrown across a room does not split into splinters that could hurt a child. A separate examiner's report describes that slip on a question like this one. Many candidates lost marks on this question because they identified properties or design features of the finished product such as the shape or texture instead of working properties of the materials used. The way to avoid it: circle the material the question gives, and underline the part it names. Then every sentence is about that material in that part, not the shape the maker gave it. Keep to the setting too: a garden table left outside needs a point about rain, not about recycling. Now the performance half, on a textile. A running top is made from polyester, and polyester fibres take up very little water. How does that property affect how well the top performs on a long run? Sweat moves through and off the fabric instead of soaking in, so the top dries quickly. The runner is not carrying a cold, heavy, wet shirt for the last few kilometres. Cotton does the same job worse, because it soaks up sweat and stays wet. That is the whole chain: the property, what it does, then how the product performs because of it.

Now the frying pan from the start of this video. The white solid Roy Plunkett found was polytetrafluoroethylene, PTFE for short, the coating sold as Teflon. Two of its properties decide its use. Very little sticks to its slippery surface, and almost no chemical attacks it. It is a polymer, but it is not just any plastic. Turn those two properties into what the pan does better. How does it perform? Food lifts off the coating instead of burning on, so eggs come out whole and the pan wipes clean. And washing-up liquid and acidic food cannot eat into it, so the coating lasts through years of cooking and cleaning.

A few questions to pull it together. Four of them, and the last one is about the pan.

A garden fence panel is described as made of wood. What is wrong with that answer? Wood is a group, not a material. The answer names the specific timber, such as pine, and then its property. Now this: aluminium is used for drinks cans because it is cheap. Which word fails, and why? Cheap. It is a price, not a property. Low density, or resistance to corrosion, would be a property. Here's a sort: because wool insulates, the hat keeps you warm all day. Use or performance? Performance. It says how well the hat works over a whole day of wear. Now the pan once more: what is its coating made of, and which property decides its use? PTFE is the coating. Very little sticks to it, so food slides off, and almost no chemical attacks it, so cleaning products cannot eat into it.

If you could now explain that pan to a friend, this one's landed, so a thumbs up marks it off on your list. If it hasn't settled yet, keep it in your saved videos, because three or four practice questions in, this way of answering starts to feel normal.

Next in the chapter: Where materials come from: sources and converting them into workable forms, the route from forest, mine or oil well to the plank or granule a maker buys. Hopefully that's next in your feed, but if not, search for ScholaFly D T oh three, oh four.

Every other video is on scholafly.com too, easy to search by video code or by keyword. Whatever you're revising, go there and have a look, or, watch the next video.