How heat gets through the walls
Heat flows through a wall at a rate set by three things: the insulating quality of the material (its thermal conductivity, k), the thickness of the material, and the temperature difference across it. Doubling thickness roughly halves the heat flow. A larger temperature difference, such as a freezer in a hot kitchen, increases it proportionally.
Good PUF has a very low thermal conductivity, typically around 0.02 W/m·K when new. That is why a few centimetres of it can do the job of much thicker layers of older insulating materials.
What thickness does in numbers
Take one square metre of wall with PUF of conductivity 0.022 W/m·K, and a freezer at −18 °C in a 40 °C room, a 58-degree difference. The heat flowing through that square metre depends on thickness as shown below. Multiply by the cabinet's total wall area to see the effect on the whole unit.
| PUF thickness | Heat flow per m² | Change vs 60 mm |
|---|---|---|
| 60 mm | about 21 W | — |
| 80 mm | about 16 W | about 25% less |
| 100 mm | about 13 W | about 40% less |
| 125 mm | about 10 W | about 52% less |
Typical thicknesses
- Chilled reach-ins and undercounters: commonly around 50–75 mm walls.
- Freezer cabinets and chest freezers: commonly thicker than chillers, often 75–100 mm or more.
- Cold-room panels: thicker panels are used for freezer rooms than for chiller rooms, with freezer panels often 100–150 mm.
- Doors and lids are often thinner than walls, which makes gaskets and door design important.
What density tells you
Density, in kilograms per cubic metre, describes how much foam material is packed into the space. Refrigeration foam is commonly in the region of 38–42 kg/m³. Density on its own does not make insulation better; past a point, denser foam conducts slightly more heat. What density does affect is strength, rigidity and dimensional stability.
Too low a density can produce foam that shrinks, leaves voids or lets panels flex, which opens gaps and cold bridges. Too high adds cost and weight without improving insulation. A properly foamed, evenly filled cabinet at a sensible density is the goal.
Quality matters more than the number
- Even filling with no voids, especially in corners and around fittings.
- Good bonding between foam and skins, so panels stay rigid.
- Minimal cold bridges: metal fasteners and frames that cross the insulation leak heat.
- Tight door gaskets; the best wall is wasted if air leaks around the door.
- A blowing agent with zero ODP and low GWP, such as cyclopentane, in modern foam.
Ageing and damage
PUF slowly loses some insulating value over the years as gases in its cells exchange with air. Physical damage is worse: a dented panel, a crack that lets moisture in, or water soaking into foam from a leaking drain can sharply reduce performance. In humid Indian conditions, moisture that gets into insulation can also freeze inside freezer walls. Keep drains clear, repair skin damage and replace failed gaskets promptly.
Frequently asked questions
- Is thicker insulation always worth it?
- For freezers and units in hot rooms, extra thickness usually pays back through lower energy use. The returns diminish as thickness increases, and thicker walls reduce internal space for the same external size.
- How can I check insulation thickness before buying?
- Ask the supplier for wall, door and base thickness separately, plus the foam density and blowing agent. Measure the door edge or lid edge yourself on a display unit; it gives a rough idea of the panel build.
- Does a glass-top chest freezer have less insulation?
- The glass lid insulates far less than a foamed lid, which is why glass-top freezers use more energy and are given separate BEE star bands. The walls and base are still foamed.
- Why does my freezer sweat on the outside?
- Sweating on the outer skin can point to a cold bridge, a void in the insulation, a failing gasket or very high room humidity. A technician can check with a thermometer or thermal camera where the cold spot is.
