Science and Technology K–6 · Year 4

Keep it cold: which wrapping slows an ice cube's melting?

Science understanding: Chemical sciences

Practical, model not builtLow risk

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

An insulating material slows the flow of heat, so ice wrapped in wool or bubble wrap melts more slowly than ice in foil or bare, which is why eskies and jumpers work.

What you need

5 ice cubes from one tray (about 20 g each), weighed
wrappings: wool sock, bubble wrap, newspaper, aluminium foil, nothing. Build each wrap up to about 1 cm thick with as many layers as it takes (fold the sock, wind the bubble wrap round more than once, crumple several sheets of newspaper) and check it with a ruler; the foil stays a single layer, because its effect comes from its shiny surface, not its thickness
5 zip bags to hold the wrapped cubes
kitchen balance reading to 0.1 g (a balance reading only to 1 g cannot separate the one layer and two layer results, which the model puts 1.1 g apart)
ruler
timer

How to do it

Weigh each cube, seal it in a zip bag and wrap it in its material. Leave one unwrapped as the control.
Leave all five on the bench for 30 minutes at room temperature.
Unwrap, pour off the melt water and weigh the ice that is left.
Work out the mass melted for each wrapping and graph it.
Repeat with two layers of the best wrapping and record the change.
Rank the materials as insulators and link the result to eskies, jumpers and house insulation.

What you should see

The bare cube loses the most ice, the foil-wrapped cube less, and wool and bubble wrap the least. A 20 g cube is 2.8 cm on a side (47 cm2 of surface); wrapped in 1 cm of wool (thermal conductivity 0.04 W per metre kelvin) the wrap's outer surface is 138 cm2, and conduction through a mean area of 80 cm2 with the room 22 degrees above the ice carries 0.71 W, which melts 3.8 g in 30 minutes. The bare cube loses more because moving air and the bench feed heat in faster than still wool does. Foil adds almost no resistance to conduction, but its shiny surface (emissivity about 0.05, against about 0.9 for the plastic bag) cuts the heat arriving as radiation: for a 3 cm object in still air 22 degrees warmer than the ice, radiation carries about 4.7 W per square metre kelvin and natural convection about 6.9, so a shiny surface lowers the heat gain through it by about 38 percent. Doubling the wool to 2 cm lowers the conduction model to 0.50 W and 2.7 g melted, about 30 percent less rather than half, because a thicker wrap around a small cube also has a larger outside surface. That is 3.8 g against 2.7 g, a difference of 1.1 g obtained from two weighings, so the balance has to read to 0.1 g for the one layer and two layer comparison to mean anything. Ice straight from a freezer at minus 18 degrees Celsius first takes in about 0.75 kJ to warm to 0 degrees, so the first minutes melt little.

What changes

What you change: wrapping material
What you measure: mass of ice melted in 30 minutes
What you keep the same: cube mass
wrapping thickness about 1 cm (the single foil layer excepted)
time
room temperature

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Foil is cold, so it cools the ice (foil feels cold because it conducts heat away from the hand quickly; its shiny surface slows the heat arriving as radiation, but it does not make cold).
Wool makes heat, so it should melt the ice faster.
Insulation stops heat completely.

Safety card

Low riskLearners carry it out

Hazards

melt water spills

Controls

bags sealed
work on trays

Note

Risk assessment before the lesson using Primary RiskAssess or the school's own template.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST2-7MW-T ST2-8PW-ST ST2-1WS-S
Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST2-PQU-01
Australian Curriculum v9AC9S4U04AC9S4H02AC9S4I02AC9S4I04

Sources

The pages the author read to write this activity.

All Concept Studio activities