Closed-cell vs open-cell insulation

Closed-cell and open-cell are the two families of foam insulation, and the difference matters enormously on anything cold. Closed-cell foam has sealed, water-tight cells: it resists moisture and water vapour, packs a higher R-value per inch, and is firm — which is exactly why elastomeric closed-cell lagging (the black rubbery type, e.g. Armacell / K-Flex) is the standard on AC refrigerant and chilled-water pipes. Open-cell foam has interconnected cells: it's softer, cheaper and good for interior sound-deadening and filling space, but it absorbs water. That absorbency is the trap in Dubai: a cold pipe or duct runs below the dew point, so humid air condenses on and into any insulation around it — put open-cell (or the wrong absorbent lagging) on a chilled pipe and it soaks up that condensation, loses its R-value, and starts dripping and growing mould, the exact 'sweating pipe' problem. Rule of thumb: cold, moisture-exposed or outdoor = closed-cell (sealed to act as a vapour barrier); interior acoustic or gap-filling where it stays dry = open-cell is fine. Manufacturers such as Owens Corning publish the properties of each. Getting the right closed-cell pipe lagging at the correct thickness — and properly sealed — is what stops Al Ghubaiba's insulation team being called back for a dripping ceiling.