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Insulation K-Value, C-Value & U-Value

On our blog, we’ve written about the R-value of insulation, which is essentially how effective an insulation material is. But did you know there is more than just R-value? Related terms are K-value, C-value and U-value.

We know, there are a lot of insulation terms that may be confusing, but insulation installation shouldn’t be a DIY project. Asking insulation professionals is always the best option, but it can help to know some basics before talking to the pros!

Insulation K-value, or K-factor, is used to rate the material’s ability to allow heat to pass through it, independent of its thickness. The lower the K-value, the better the insulator.

Insulation C-value, or C-factor, is used to rate thermal conductance; it’s the number of BTU (British thermal units) that pass through a square foot of material with a 1 degree temperature difference for a specified thickness. The lower the C-value, the more effective the insulation.

Insulation U-value is known as thermal transmittance, which refers to the heat transmission through an area of a material construction, induced by temperature differences between the adjacent environments. The lower the U-value, the better.

It can be tough to put insulation terms like these into layman’s terms, but what you basically need to know when it comes to insulation U-value, K-value and C-value is that:

  • A lower U-value (which can kind of be thought of as temperature difference between adjacent areas) indicates more effective insulation.
  • A lower C-value means the insulation performs better—and the same thing with a higher R-value.
  • The lower the K-value, the greater the insulating value for a particular thickness and given set of conditions.

How Effective Is Insulation?

In addition to the U-value, K-value and C-value, the type of insulation can determine the effectiveness of insulation, depending on what your goals are. For example,

  • Loose-fill cellulose and fiberglass insulation are the best at soundproofing.
  • Spray foam insulation is very effective at reducing air infiltration.
  • Radiant barrier helps your home stay cool in the summer, by reflecting heat from the sun and is especially cost-effective in warm climates (like here in California).

To learn more, contact the experts at Gold Star Insulation!

Where should you insulate in your home? Check out our interactive infographic:

Products We Install
Energy Audits

Our team can help you save money with a home energy audit and air sealing services.


Our insulation team installs batt and blown-in fiberglass insulation.


Environmentally friendly and effective, cellulose works well in homes and buildings.

Spray Foam

Gold Star Insulation is a leading installer of spray foam insulation in the Sacramento area.

Radiant Barrier

An attic radiant barrier can help keep your home cooler and more comfortable.

Insulation Removal

Gold Star Insulation provides home insulation removal services.

Air Sealing

We are committed to saving you money by sealing your attic—which is the main source of air leaks in the home.

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