Possible Clues:

• Falling behind
• Insulating material
• Trailing behind
• Jacket to wrap around a boiler to prevent heat-loss
• Insulation — failing to keep up
• Trailing insulation
• It's used to wrap around boilers, say, to prevent heat-loss
• Not up to date with thermal insulation?
• Wrapping used to prevent loss of heat
• Falling behind with winter weather precautions