&bulla new iridescent plastic that reveals hidden images with a breath is described in a recent paper published in advanced materials.&bullresearchers at the university of michigan hope to use this technology for anticounterfeiting purposes, replacing the ubiquitous hologram stickers used on things like luxury handbags and passports with a humidityactivated logo.&bulltheir surface is studded with a grid of columns, called nanopillars, each 100 times thinner than a human hair.&bullwater droplets scatter incoming light, destroying the intricate interference responsible for its shimmering colours. the researchers accidentally rediscovered this phenomenon when one of them breathed on an iridescent sheet and it became more transparent. &bullwhen you breathe on the sheet, water condenses on the sheet and makes it transparent, everywhere but on the outline of the image. 
