Keeping drugs, and particularly vaccines, potent in tropical climes is a challenge. Heat tends to damage them. Such medicines have therefore to be passed from one refrigerator to another, along what is referred to as a cold chain, until they arrive at the clinics whence they are to be deployed. Fridges, however, are expensive. They also require electricity, which is not always available—or is available only unreliably—in the poorer parts of the world. As a consequence, breaks in cold chains are reckoned by the World Health Organisation to destroy almost half of the vaccines produced around the world.

Some vaccines can be freeze-dried, which helps. But even treated thus, their lifetime out of the fridge is limited. Ways of keeping drugs and vaccines stable at tropical temperatures would therefore be welcome. And David Kaplan of Tufts University, in Massachusetts, thinks he has found one. Put simply, he and his colleagues have worked out how to pack medicines in tiny silk pouches, in a manner that makes them almost indifferent to heat.