The Plastic Chair review – a history of the world’s most sat-on object, with a sting

There is a reasonable case that the most successful piece of design in human history is a white plastic garden chair. The monobloc, moulded in a single shot of polypropylene in under a minute, has been made in quantities nobody can count, a billion is the figure the Design Museum settles on, and is sat on in cafes, weddings, refugee camps and parliaments on every continent. It costs about £3. It will outlast the people who buy it by some centuries. The Plastic Chair, which opened in Kensington on Friday, is the first serious museum exhibition to take it seriously, and it is a good one.

The curator, Lena Marchetti, begins not with the monobloc but with its ancestors: the 1960s Italian and Danish experiments in injection-moulded furniture, the first all-plastic chair designed for children, and a wall of failures, chairs that cracked, sagged or cost more than the wooden ones they were meant to replace. The exhibition is excellent on the engineering, with a cutaway mould, a film of a chair being made in 55 seconds in a factory in Lancashire, and a section explaining why the monobloc’s particular curve, which looks like a style decision, is in fact what stops it collapsing.

The middle rooms are a tour of the chair’s afterlife: hacked, stacked, painted, repaired and, in one memorable photograph from a street market in Lagos, used as currency. A room of 40 monoblocs from 40 countries, almost identical and subtly not, is the exhibition’s cleverest idea; the differences, a slightly higher back here, a drainage hole there, are a map of local manufacturers quietly adapting a global design without asking. There is a chair from a Welsh rugby club with the club crest moulded in. There is one from a Bulgarian wedding with the bride’s name in marker pen.

What the exhibition does less well is the thing it leaves to the final room, which is the plastic. The monobloc is close to unrecyclable in practice, it degrades in sunlight into fragments, and the exhibition knows this: there is a case of microplastic samples, a chart, a few lines of text. But having spent five rooms being charmed by the object, the show cannot quite bring itself to indict it, and the final room has the feel of a disclaimer. A braver exhibition would have put the chart at the start.

The exhibition design, by the London studio Hollow Form, is appropriately cheap-looking in a considered way, with the chairs displayed on stacked pallets and the labels printed on polypropylene, and visitors are invited to sit on the exhibits, which they do. The catalogue, a brick of a thing at £35, is better than the show on the environmental question and worth having.

Marchetti says in her introduction that she wanted to make an exhibition about “the design the design world does not talk about”. She has. She has also, perhaps unintentionally, made one about the design world’s ability to find a way of not talking about the parts that hurt.

The Plastic Chair is at the Design Museum, London, until 8 March.