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Current Situation and Development Trend of Insulating Glass Sealant

The insulating glass was invented in 1865 by American Mr. T.D. Stetson applied for a patent (patent number 49107). In the following period of more than 100 years, the development of insulating glass was very slow; during this period, the sealing structure of insulating glass underwent welding, welding, snap-fitting, and gluing. The main reason for the rapid development of insulating glass is the appearance of polysulfide glue and its wide application in insulating glass. After single-channel sealing was first used in the bonding method, to improve the sealing life of the insulating glass, people began to use the double-channel sealing structure. For example, in the mid-1970s, the proportion of insulating glass single-pass sealing accounted for nearly 80% of the insulating glass sealing structure in the United States at that time. During the same period, the types of insulating glass sealants and their market share have also changed, from the dominance of polysulfide rubber to the emergence of polyurethane in the 1980s, and gradually rose, until 2002, when the global insulating glass polyurethane dominated polysulfide. The phenomenon of a sharp drop in glue. In addition to these conventional sealants, in the mid-1990s, some major insulating glass sealant manufacturers in the United States independently developed new insulating glass sealants, that is, reactive moisture-curing hot melt adhesives.

The purpose of this article is to describe the basic content of the sealing structure of insulating glass, discuss the changes in the market share of insulating glass sealants and their reasons, the concept, characteristics, and advantages of new sealants, including physical, economic and technological aspects. 

Finally, this article also predicts the development trend of foreign insulating glass sealants. Through the discussion, readers can understand the change process, current situation, and development trend of insulating glass sealing structure abroad, to actively grasp the structure of insulating glass sealant in my country, the production of sealant, and the research and development of new products, to adapt to the society Demand for high-grade insulating glass.

 Insulating glass sealing structure

The adhesive sealing structure of insulating glass mainly includes single-channel sealing and double-channel sealing, as well as the DSE (equivalent to double-channel sealing) structure that appeared in the mid-1990s.

1.1 The double seal

The function of the first sealant.

(1) Pre-positioning of insulating glass;

(2) Isolation of water vapor

(3) Prevent air and inert gas from entering and leaving the hollow glass cavity. 

Among the currently used insulating glass adhesives, butyl rubber (PIB) has the lowest water vapor permeability rate (MVTR) and is therefore usually used as the first seal.

The role of the second sealant.

(1) Bond the glass and the spacer into a whole insulating glass;

(2) Prevent the leakage of molecular sieves outside the school;

(3) Elastic recovery and buffer edge stress;

(4) It plays an auxiliary role in preventing the penetration of water vapor. 

Figure 1 the insulating glass double sealing

Figure 1 the insulating glass double sealing

1.2 Common spacer systems for double seals

Metal spacer

The first seal: Butyl rubber (PIB)

Second Seal: Polyurethane, Polysulfide, and Silicone

Super spacer

The first seal: Super spacer

Second seal: Conventional hot-melt butyl adhesive, reactive hot-melt adhesive

PVC or fiber glass spacers

The first seal: Butyl rubber (PIB)

Second Seal: Polyurethane, Polysulfide, and Silicone

Swiggle Strip

The first seal: Swiggle high glue strip

Second seal: Silicone glue

From the above analysis, the sealing life and durability of insulating glass require double sealing for insulating glass. The functions of the first seal and the second seal are different, and they each perform their duties and cannot replace each other. The practice has shown that the durability and sealing life of double-sealed insulating glass is longer than that of single-channel sealing.

Figure 2 The insulating glass swiggle strip

Figure 2 The insulating glass swiggle strip

1.3 Common spacer systems for single-pass seals

are as follows:

  • Aluminum spacers and hot melt butyl
  • Aluminum spacer and polysulfide
  • Aluminum spacers and polyurethane
  • Real-dimensional high glue strip
  • Evolution of European insulating glass sealant systems

In Europe, double seals have always dominated. According to statistics, in 1990, double-channel sealing accounted for 90% of the overall insulating glass market share, and in 2002 its market share was still 90% with no change. But over the same period, single-pass seals dropped from 8% in 1990 to 2%. See Table 1.

1990 year2000 year
Double sealed metal spacer system90%90%
Single-lane sealed metal spacer system8%2%
Warm Edge Spacer System2%8%
Table 1 The Market Share Distribution of Insulating Glass Sealant Systems in Europe

1.4 Single seal

Different from the European market, as of 2000, the market share of single-pass sealing in the US insulating glass was about 20%. The American Insulating Glass Manufacturers Association (SIGMA) has tracked the use of insulating glass in North America for 20 years, showing that double sealing is positively correlated with the sealing life of the insulating glass. However, the sealing failures of insulating glass produced in the United States each year account for 5% of the total, the most important of which is single-pass sealing!

Why do single-pass seals have a larger share in North America than in Europe?

move relatively frequently or not

Residents in Europe live relatively stable life. Therefore, they attach great importance to the energy saving of the windows of the houses they live in, especially the durability and airtightness. In contrast, residents in North America move many times in their lives, and each time they move, they may decide whether to update the windows depending on the specific conditions of the doors and windows. Relatively speaking, unless the move is a permanent residence, the shelf-life requirements for updated windows will be lower than those in Europe.

From the point of view of production use

The main purpose of using hot melt butyl rubber (HMB) and Swiggle Strip is the convenience of production and use. Most of the door and window manufacturers in the United States have their insulating glass lines, which are matched for themselves, and mostly use horizontal lines, which require simple processes and can be quickly transported and installed. The production of insulating glass in Europe is a mainly vertical line, which is matched for door and window manufacturers, so double-channel sealing is adopted.

From the scope of use

In the United States, single-pass sealing is mainly used in temperate regions. The testing standards for insulating glass in the United States are also relatively loose, making it easier for insulating glass with a single-channel sealed structure to pass the test. Europe is more cautious, and northern Europe has lower temperatures in winter, and the standards tend to be consistent.


Because of the short sealing life of single-channel sealing, which cannot meet people's demand for high-grade insulating glass, manufacturers have to abandon single-channel sealing and adopt double-channel sealing to improve the sealing life of products. However, in terms of specific practices, the paths taken by Europe and North America in adopting double seals are different. The transition from single-pass sealing to double-pass sealing involves a structural transition of insulating glass. This structural transition occurs mainly in Europe, followed by North America. 

There are two main forms of double seal structure:

Butyl + Polyurethane or Polysulfide or Silicone

Super spacer + hot melt butyl glue (regular or reactive)

Reactive hot-melt adhesive and equivalent to double seal

The purpose of research and development of reactive hot-melt adhesive: Conventional hot-melt butyl glue is mostly used for the single-channel sealing structure of insulating glass, which has the advantage of convenient production. On the other hand, when conventional hot-melt adhesives are mostly used for single-pass sealing, they lack structural strength, resulting in short durability and short sealing life of the insulating glass. The single-channel sealing structure using conventional hot-melt adhesive cannot meet people's requirements for improving the sealing life of the insulating glass and must be changed. But people in Europe and North America adopted a different approach. In Europe, people are moving from single-pass seals to warm-edge double-pass seals such as Thermoplastic Spacer Bars (TPS) and dual-pass seals for Super Spacer Bars. However, in North America, people are exploring and developing a new type of sealant, which has the advantages of convenient production of conventional hot-melt adhesives and low water vapor permeability, and at the same time has the advantages of two-component sealant structural adhesives. Under such logical thinking, some insulating glass sealant manufacturers in the United States independently researched and developed reactive hot melt adhesives from 1995 to 1996, aiming to solve the problem of sealing failure caused by ordinary single-pass sealing.

The concept, features, advantages, and equivalent double sealing concept of reactive hot melt adhesives. 


Reactive hot-melt adhesive is a one-component, heating glue, chemical curing insulating glass sealant.


Three major categories: According to the difference in base glue, reactive hot melt adhesive is divided into three categories, namely reactive hot melt polyurethane, reactive hot melt butyl adhesive, and reactive hot melt modified silicone adhesive.


One-component chemical curing (moisture curing)

Has the characteristics of two-component glue

Has the characteristics of conventional hot-melt butyl rubber

Structural strength is greater than other one-component sealants

Equivalent to a double seal

What is the difference with two-component glue?

One-component glue:

  • A variety of glue dispensers are available: 55 gallons, 5 gallon, and block glue dispensers
  • The glue temperature is lower
  • Low water vapor permeability
  • Low inert gas permeability
  • No waste: glue mixing test, glue removal, etc.

Comparison with conventional hot melt butyl rubber 

The difference

"One-component glue" ≠ one-component glue

Thermo setting adhesive, chemical curing, moisture curing, elastic material; also has the characteristics of double sealant; lower glue temperature

Thermoplastic, physical curing, non-elastic materials; mainly play the role of airtight single-channel sealant 

The same

A variety of glue dispensers are available: 55 gallons, 5 gallon, and block glue dispensers. Maybe the Jinan LIJIANG Glass manual insulating glass two-component sealant sealing machine is your best choose.

Low water vapor permeability

Low inert gas permeability

No waste: mixing test, extrusion, etc.

manual insulating glass two-component sealant sealing machine

Equivalent to double seal?

The concept equivalent to double sealing was proposed by Pittsburgh Flat Glass (PPG) Company, which refers to the reactive hot melt adhesive used for its patented U-shaped spacer.

According to the definition of American PPG company, reactive hot melt adhesive is a one-component, hot glue, moisture chemical curing sealant. The equivalent double seal includes two aspects: structural equivalence and economic equivalence.

Structural Equivalence

Structural equivalence needs to pass the following inspections: Seal Life: At least 85% of products pass CBA inspection

CSTB Shear Test: Passed at high temperature

Argon gas retention rate: maximum annual leakage rate of 1%

Vertical storage for 1 month: Pass the continuous drop test for 1 month (-29—49°C): Pass the CSTB climate cycle test: Pass the independent laboratory test report

Economic equivalence

Equivalent to the double sealing cost of producing standard insulating glass

Supported by published data

Figure 3 The insulating glass single sealing

Figure 3 The insulating glass single sealing 

1.5 Production process equipment

The automatic insulating glass glue process equipment is the same as the process equipment used for conventional butyl rubber glue

Automatic Insulating Glass Vertical Sealing Robot Machine

If it is said that the single and double seals of insulating glass are investigated, the macroscopic structure of insulating glass is investigated, and the different influences between them on the durability and sealing life of insulating glass are analyzed. Then, after examining the situation of single-pass sealant for insulating glass, let's take a look at the change in the market share of double-pass sealant for insulating glass, and analyze the change in its internal microstructure. Table 2 shows the change in the European market share of the second insulating glass sealant. As can be seen from the table, in 1990, the market share of polysulfide rubber was 83%, polyurethane was 6%, hot-melt adhesive was 3%, and organic warm edge system was 2%. In addition, there has also been a slight increase in conventional hot melt adhesives and organic warm edges for secondary seals over the same period.

PolysulfidePolyurethaneHot melt glueSilicone glueOrganic warm edge
1990 year83%6%3%6%2%

Table 2 Changes in the European market share of the second insulating glass sealant

It should be pointed out that the large rise of polyurethane and the decline of polysulfide are not accidental. A similar phenomenon occurs in the insulating glass market in North America. In 2001, polyurethane and polysulfide each accounted for 50% of the market share, but a year later, in 2002, polyurethane increased sharply to 80% of the market, and polysulfide dropped to 20% accordingly.

2001 year50%50%
2002 year80%20%
Table 3 Changes and development trends of polyurethane market share in North America

2001 year20%80%
2002 year40%40%
2004 year 80%20%

Table 4 The change and development trend of polyurethane market share in Europe

Reason for change

Below we analyze the reasons for the changes in the market share of insulating glass sealants. We believe that there are two main reasons for the increase in the use of polyurethane sealants, including basic reasons and fuses.

American Morton Company is the largest manufacturer of polysulfide collagen in the world. The company's parent company, American Rohm & Hass Company, officially announced on April 26, 2001, that the company decided to officially close its factory in Moss Point, Mississippi, USA at the end of 2001 to stop producing insulating glass polysulfide rubber.

According to R&H company's explanation, the reason that influenced R&H company to launch the production of polysulfide rubber is

  • Negative growth in sales and sales volume;
  • Competing products and technologies;
  • environmental protection;
  • and the substantial investment required to achieve acceptable manufacturing standards.

Consequences of discontinuation

Morton's production of polysulfide collagen accounts for 2/3 of the world's. This decision to stop production means that 2/3 of the polysulfide rubber will disappear from the global market, which will have a huge and far-reaching impact on the production of insulating glass in the future.


Faced with the disappearance of 2/3 of the polysulfide collagen in the insulating glass market, the European market and the North American market have adopted two completely different countermeasures. In Europe, double-pass sealing of insulating glass dominates. Therefore, when the production of polysulfide rubber is greatly reduced, many companies have adopted the practice of replacing polysulfide rubber with polyurethane.

Although the reduction of the global supply of polysulfide rubber by 2/3 is an important reason for the sharp rise in polyurethane, we think that if it is not for the improvement of polyurethane with excellent quality, it will not replace polysulfide rubber in such a short time. The latter is the basic reason for the increase in polyurethane. 

Specifically as follows:

1. The water absorption capacity of polyurethane and the swelling of colloid after water absorption are smaller than that of polysulfide rubber

Water absorption capacity and colloidal swelling of different sealants

Experimental method: Immerse the sealant in water at a temperature of 60°C for two months.

Weight gain

  • Polysulfide rubber 30%
  • Polyurethane glue 12%
  • Silicone glue 2-6%

Volume increase

  • Polysulfide rubber 50%
  • Polyurethane 15%o Silicone glue 3-10%

2. After the polyurethane is cured, the sealant does not shrink, especially at the corners; after the polyurethane sealant is cured, there is no shrinkage, so there is no reduction of water and gas channels.

3. Polyurethane does not produce glass stress caused by glue shrinkage

As the solvent evaporates from the edge-sealed colloid (such as polysulfide), although the sealant still maintains full contact with the glass, the stress generated by the shrinkage of the colloid becomes the stress applied to the glass. Stress fulcrum action. The effect of stress depends on the thickness of the glass, the size of the air spacer, and the size of the insulating glass, and is most pronounced for the original glass and the large spacer. This stress can be reduced by the relaxation of the sealant, which increases the water vapor transmission area of the insulating glass, or it becomes permanent stress resulting from glass deflection. This stress increases the likelihood of the glass sheet cracking in the first winter after installation, because the insulating glass will deflect inwards in winter, reducing the "first winter" of the insulating glass

Seasonal "breakage" possibility. Reports from some countries with severe climates show that the insulating glass made with solvent-free polyurethane glue has a breakage rate of 0.5% during production and "first winter" to close to zero.

4. No special requirements for storage and handlingUsually, the solvent added to the polysulfide glue, such as toluene, methyl and ethyl ketone, etc., is flammable, which leads to a decrease in the ignition point of the glue after mixing. The ignition point of polyurethane insulating glass glue is greater than 93.3 ℃.

5. Does not contain organic volatile solvents, so there is no need to use a desiccant that adsorbs solvents. In contrast, when using polysulfide rubber, the solvent can consume 5% to 10% of the adsorption capacity of the adsorbent.

6. Better performance of adsorbent. Since it is not necessary to consider the presence of volatile solvents when selecting adsorbents, the use of polyurethane insulating glass makes the selection of desiccants easier. Since the solvent may exist in the insulating glass-like water vapor, most of the above adsorbents can absorb solvent gas from the sealant.

7. Reduce glass breakage during production. Since solvent volatilization produces stress on the glass, if the stress is too large, the glass may be broken for single-strength insulating glass with large stacks and medium-to-large air gaps. When the glass stack is cut away, only one piece of the 30-piece glass stack may be broken, or it may be a small percentage. When the edge sealant is a solvent-free urethane glue, the cracking of the glass during production is greatly reduced. This reduction is independent of other variables such as glass deflection and breakage.

8. Compared with polysulfide rubber and silicone rubber, the water vapor permeability of polyurethane is the lowest. Under the condition that other conditions remain unchanged, the sealing life and durability of insulating glass made of polyurethane should be longer.

After analyzing the physical and chemical characteristics of polyurethane, it is necessary to look at its production cost and process to complete the analysis of the basic reasons for polyurethane replacing polysulfide rubber.

From a cost perspective,


Calculated by weight, the price is slightly lower than that of polysulfide rubber;

Calculated according to the material saved in production, it is about 10% lower than that of polysulfide rubber;

Therefore, under the condition of using the same butyl glue, the production cost per unit of insulating glass is saved by more than 10%.

Reactive hot-melt adhesive

Not more than the cost of a double sealant (butyl + polysulfide)Conventional hot melt butyl with little extra single seal

From the point of view of the production process,

Polyurethane process equipment, existing polysulfide glue equipment modification, modification fee < US$8,000

Process equipment for reactive butyl rubber, common to hot melt gluers

The development trend of insulating glass sealant

Double seal increases

Polyurethane rises, and reactive hot melt adhesive rises. Polyurethane market share continues to increase. Within two years, the ratio of polyurethane to polysulfide rubber in the European market will be changed from the current 1:1 to 4:1.

Reactive hot melt adhesives increase. In Europe, where the traditional double-pass sealant is used, the development and production of reactive hot melt adhesives have also begun. For example, reactive hot-melt adhesives have begun to appear in Europe this year, and the manufacturer is the French Le Gevre sealant company.

Polysulfide drop

The single-pass seal drops further but doesn't disappear completely. Because, there are always some manufacturers who use single-channel sealants for one reason or another, such as to meet certain market requirements.

In addition, new reactive hot melt adhesives will enter the market in the next few years, UV curing, infrared curing, and moisture curing including heat reactive melt polyurethane, reactive hot melt butyl, and reactive hot melt modified silicone Ketone glue.

For more information about Jinan LIJIANG Glass insulating glass processing equipment and insulating glass processing accessories, please click here to learn more. 

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