Scientists say 200 million of the cards, which cannot be seen by the naked eye, could fit inside a single postage stamp.

Scientists in the UK have unveiled the world’s smallest Christmas card.

Produced by the National Physical Laboratory (NPL), the tiny Christmas card measures just 15×20 micrometres – thinner than a human hair.

The card is so small it requires a powerful microscope just to be seen, never mind reading the festive inscription inside.

It is made from platinum-coated silicon nitride, a common material in electronics, and is over 10x smaller than the previous record-holding smallest Christmas card, which measured 200×290 micrometres.

The design and message on the card were carved using a focused ion beam – “a jet of charged particles”, according to NPL.

A micrometre is one millionth of a metre (0.000001m) and is displayed with the symbol µm.

More than 200 million of the minuscule cards could be fit inside a single postage stamp, NPL said.

In a cubic metre, similar to the size of a post box, you could fit 7 quadrillion (7,000,000,000,000,000) of these cards – roughly 900,000 for every person on Earth

Dr David Cox, research fellow at NPL, who created the card with his colleague Dr Ken Mingard, said: “While the card is a fun way to mark the festive season, it also showcases the progress being made in materials research on this scale.