Question

For keeping goods cold during shipment , what is an advantage of dry ice?

Answer 1

-- Although it has lower specific heat than regular ice, dry ice is colder.
So you have to use more of it to soak up the same amount of heat, but
if there's enough of it, it can keep the goods colder during shipment than
regular ice can.

And here's ANOTHER advantage, at no extra cost:

-- Dry ice doesn't melt and become liquid. It 'sublimes' and becomes gas.
Regular ice leaves water, which soaks through the shipping carton, makes
a puddle on the floor, and leaves a mess. Dry ice turns to gas, drifts away
on the breeze, and leaves nothing.

Answer 2

Dry ice doesn't technically melt. It becomes a gas (carbon dioxide) which allows the goods not to become wet and the box not to get wet and weak.