How To Choose The Material of Thermal Break Strips For Windows And Doors?

What is thermal break strip?

Thermal break strip is an important component of thermal bridge broken aluminum windows and doors. And the main function of thermal break strip is thermal insulation.

Thermal break strips are widely used for their ability to block heat conduction. The quality of the thermal break strip not only determines the thermal insulation effect of windows and doors, but also has a fundamental impact on the wind pressure resistance, water tightness, air tightness, etc. of windows and doors. The thermal break strip also determines more than 50% of the insulation effect of windows and doors.

At present, there are three common material of thermal break strip on the market:

• PA66
• PVC
• PU

Both PA66 thermal break strip and PVC thermal break strip are suitable for strip insertion processing technology(as show in Figure 1).

PU thermal break strip are suitable for Pour & Debridge processing technology(as show in Figure 2).                                     

                                         Figure 1  strip insertion                                                            Figure 2  Pour & Debridge

Today we are going to talk about the thermal break strips which suitable for strip insertion processing technology. That is PA66 thermal break strip and PVC thermal break strip.

The main differences between these two are as follows:

1. Different Material

• PA66 thermal break strip is made of PA66 and 25% glass fiber.
• PVC thermal break strip is made of PVC and 25% calcium carbonate.

2. Different Appearance

• PA66 thermal break strip has a brighter, darker black hue. PA66 strip has smooth and flat surface and it looks more like frosted texture(as show in Figure 3). There are gear marks pressed from the puller at both sides(as show in Figure 4).
• The color of PVC thermal break strip should be lighter, usually grayish black. Compared to PA strip, the surface of PVC strip looks not so smooth. There may be a feeling of pits when viewed from the side. There are no gear marks at both sides.

                                                                  Figure 3  Different surfaces between PA66 strip and PVC strip

Figure 4  Different side surfaces between PA66 strip and PVC strip

3. Different Toughness

• PA66 thermal break strip can be broken after being folded for 1-2 times. There will be a clear and crisp sound when broken. After breaking, the fracture is neat and not deformed(as show in Figure 5). And strips can be restored through docking(as show in Figure 6).
• PVC thermal break strip is soft, easy to bend, and not easy to break. It needs to be folded in half for more than ten times before breaking. After breaking, the fracture becomes white, deformed. Strips cannot be restored through docking.

Figure 5  Different fracture surfaces between PA66 strip and PVC strip

Figure 6  Different joints between PA66 strip and PVC strip

4. Different Thermal Deformation Temperature

• PA66 Thermal Break Strip: around 240℃
• PVC Thermal Break Strip: around 90℃

5. Different Tensile Strength

• PA66 Thermal Break Strip ≥ 120N/mm
• PVC Thermal Break Strip: around 70N/mm

6. Different Flammability

• The PA66 thermal break strip will continue to burn after leaving the ignition source(as show in Figure 7), and it smells like burning feathers. But adding flame retardants to the raw materials can make PA66 thermal break strips have the function of Flame retardant performance.
• The PVC material has non flammability. When it leaves the ignition source, the PVC thermal break strip will automatically extinguish, accompanied by the black smoke and the smell of pungent plastic(as show in Figure 8).

Figure7  Ignite PA66 thermal break strip

Figure8  Ignite PVC thermal break strip

7. Different Photothermal Sensitivity and Aging Resistance

• PA66 thermal break strip can also maintain its stability in the direct sunlight. It’s durable, not easy to be aging.
• PVC thermal break strip is easy to become brittle at room temperature and high temperature, which means it is easy to break and easy to be aging after exposure to the sun.

8. Different Linear Expansion Coefficient

• The linear expansion coefficient of PA66 thermal break strip is (2.3-3.5)*10^-5
• The linear expansion coefficient of PVC thermal break strip is 8*10^-5

The linear expansion coefficient of aluminum profile is 2.35*10^-5

The closer the linear expansion coefficient is, the more possible that the two materials will keep synchronized expansion and contraction when the environmental temperature changes. So as to ensure the integrity of the thermal break strip and aluminum profile structure.

Comparing the two, PA66 thermal break strip has stronger thermal insulation properties, more stable performance, and is not easily deformed.

When choosing thermal break strips, it is recommended to choose PA66 thermal break strip.

The selection method is to follow the above methods to judge whether the appearance is smooth, what color it is, whether it is easy to break, and whether there is strange smell when burning.