The product is a powder, based on cornflour, which thickens to form a custard-like sauce when mixed with milk and heated.

[1] John Monkhouse (1862–1938) was a prosperous Methodist businessman who co-founded Monk and Glass, which made custard powder and jelly.

Monk and Glass custard was made in Clerkenwell and sold in the home market, and exported to the Empire and to America.

[citation needed] "Instant" versions (containing powdered milk and sugar and requiring only hot water) and ready-made custard in tins, plastic pots and cartons have also become popular.

A suspension of uncooked custard powder (starch) in water, with the proper proportions, has the opposite rheological property: it is negative thixotropic, or dilatant, which is to say that it becomes more viscous when under pressure.

The popular-science programme Brainiac: Science Abuse demonstrated dilatancy dramatically by filling a swimming pool with this mixture and having presenter Jon Tickle walk across it.