Yet another frosty glass query: Fred Weiss of Baltimore noticed frost inside his car windows in the evenings in Vermont: "This never happened in Baltimore. The temperature ... was in the teens. Can you explain this?" My new thermal engineering consultant, Nelson Hyman, discounts "maple syrup vapor" theories. He blames very cold glass, coupled with humid interior air. Water vapor touches glass cooled to the dew point, and you get dew/frost - in Vermont or Baltimore.