Ecological window filler from sheep's wool

Construction Foam Alternative

Bonding, sealing, filling - installation foam, better known as PU foam, is almost indispensable in the building industry. Nevertheless, construction foam often comes under heavy and justified criticism due to the harmfulness of its ingredients. Especially regarding the topic of sustainability, calls for ecological alternatives are becoming more and more significant. More emphasis is thus being placed on this in project tenders. In order to be shortlisted, suppliers must be equipped and able to offer alternatives in window installation, amongst other things.

  • What ecological alternatives are there?
  • What advantages do they offer?
  • What still speaks for or against installation foam?

We answer all these questions today and offer an objective overview of the pros and cons of installation foam as well as possible alternatives.

Why an alternative to building foam?

Every year, more than 200 million cans of assembly foam are sold in Europe. The functionality, ease of use and wide range of applications of PU foam make it a popular choice. The product has been on the market since the 1970s. Whether as rigid or flexible foam, it is used in the most diverse areas of our daily lives: furniture upholstery, car seats, cold insulation, insulation of electrical components and much more. However, there are also downsides to the use of this product, therefore there is a lot to be said regarding alternatives.

Respiratory health Respiratory health

PU stands for polyurethane, which forms the basis for assembly foam. Isocyanates (MDI) in turn form a base material for PU foam. And it is precisely these isocyanates that can cause allergies and can irritate eyes, skin and respiratory tracts. It is also suspected of being carcinogenic. The hazard statement H351 stands for this.

Emissions occur during processing. Only afterwards, when the substances have reacted and when there are no more monomers, is it safe for human and environmental use. For this reason, there was a self-service ban on the sale of PU foam cans in Germany until 2017.


PU foam hazardous waste PU foam hazardous waste
Sustainability and the environment

If you value healthy and sustainable building, it is certainly not wrong to look for ecological alternatives to building foam, as artificial or toxic substances are often included in its ingredients. Fortunately, the harmful blowing agent HFC is now hardly ever used.

However, it should still be noted that PU assembly foam is made from petroleum. For about one cubic metre of polyurethane, a shocking number of 70 litres of petroleum are needed. The production of the basic material requires a lot of energy

Legal requirements Building foam Legal requirements Building foam
Legal requirements

Since 2005 there has been an updated DIN 18355. The new regulation is part of the "Vergabe- und Vertragsordnung für Bauleistungen" (VOB) in Germany. It states that connection joints should be filled with mineral wool instead of PU foam. The reason is the better adaptability to possible expansions of the materials to be joined.

An EU regulation that came into force in 2020 stipulates an EU-wide training obligation for the handling of products with diisocyanates from August 2023. A note to this effect on the packaging will be mandatory from 2022.

In contrast to insulation foams for refrigerators and household appliances etc., which are often not flame-retardant, PUR insulation foam in the building sector must be flame-resistant. Hexabromocyclododecane (HBCD), which was previously used in polystyrene insulation foam as a flame retardant in combination with a synergist (dicumyl peroxide), was banned from 21 August 2015 in accordance with the European chemical regulation REACH. It has been replaced by alternative flame retardants such as pFR. They make insulating foam normal to flame-retardant (class E according to DIN EN 13501-1 or building material class B2 according to DIN 4102).


Tender construction project Tender construction project

More and more project tenders focus on sustainable construction. This is also the case for MA 34, the construction and building management department of the city of Vienna. They are currently discussing whether bidders must always offer an alternative to synthetic PU foam for window installation in projects of the City of Vienna.

The trend in this direction is increasing. In the near future, ecological alternatives will probably be an unavoidable requirement. The sooner suppliers start looking around, the better.


Assembly foam, its advantages and disadvantages

In 1937, polyurethanes began to be synthesised and further developed until polyester foam finally became established in the mid-1950s. Nowadays, it is hard to imagine the building industry without PU foam. In our neighbouring country, Germany, for example, around 80 percent of windows are insulated with use of assembly foam. And for good reason, for it is precisely during window installation that the advantages of PU foam are highlighted:

Compared to other insulation materials, PU foam has the best thermal insulation. Due to its easy handling, it is quickly processed and, due to its expansion during drying, it adapts perfectly to its surroundings, thus reaching even the unreachable nooks and crannies. Another plus point is its strong adhesive power. It creates a secure bond for windows, window frames and materials such as concrete, wood, metal and other plastics.


Let’s take a closer look at PU foam:

Advantages of PU foam

What does PU foam have to say for itself?

PU foam advantages PU foam advantages
  • Easy handling and processing
  • Reaches and seals places that are not easily accessible
  • Excellent insulation values
  • Good insulating properties even for electrical components
  • Low thermal conductivity (0.030 - 0.040 W/(mK))
  • Cures quickly
  • Expands during curing and thus adapts ideally to its environment
  • Low cost
Disadvantages of PU foam

What are the arguments against assembly foam?

PU foam disadvantages PU foam disadvantages
  • Ingredients harmful to health (isocyanates).
  • Partially contains propellants such as HFCs, which are harmful to the ozone layer
  • Petroleum-based production
  • High waste production (take high time expenditure into account)
  • Disposal according to type is often difficult due to a high adhesive effect and the resulting material compounds; disposal is only possible with a high chemical or mechanical effort.
  • UV radiation can cause breakage
  • Air and gas-permeable

What are isocyanates, MDI for short?

MDI stands for the chemical methylene diphenyl diisocyanate. Since 1 December 2010, PU foam with an MDI content above 1 percent must be labelled accordingly.

Why harmful to health?

The chemical is dangerous because it can irritate the mucous membranes, eyes and respiratory tract. Even if it no longer escapes after processing, one must work with the foam first.

Are there alternatives to PU foam?

Synthetic alternatives

Synthetic alternatives include plastics that are chemically produced.

They are usually made of petroleum, bakelite or silica, which is then further processed. This is precisely why they are often criticised as being unsustainable alternatives. They are available as boards or also as granulate for blow-in insulation.

  • Expanded polystyrene, or EPS for short, better known as Styropor, is one of the most used synthetic insulation materials.
  • Closed-cell round profiles made of polyethylene are also alternatives for sealing. They are dimensionally stable, free of blowing agents and do not absorb water.
  • There are also so-called multifunctional sealing tapes. However, these often reach their limits due to the construction tolerance and the permissible joint width and the subsequent "blower door measurement".
Styrofoam as a synthetic alternative Styrofoam as a synthetic alternative

Ecological alternatives

If you look at ecological alternatives, the choice seems to have increased, especially in recent years. The clear focus is on the environment and sustainability. We have taken a closer look at the ecological alternatives:

PU foam PU foam
Ecological building foam without isocynates

In the meantime, there are building foams in which isocyanates are partially or completely dispensed with. These are labelled with an EC1-Plus seal. However, it should be kept in mind that this is an industry quality label, which means that after 30 days, no more vapours are emitted.

Cork filler as an ecological alternative Cork filler as an ecological alternative
Cork filling material

Solvent-free dispersion spray cork is a good alternative, especially for sound and heat insulation of connection joints. In outdoor areas, an elastic sealant must also be applied to protect against the weather. The advantages of this alternative are that no chemical substances are released, it is environmentally friendly, permanently stable and tight. However, the high costs, poor thermal conductivity (0.054 W/(mK)) and the sometimes long transport routes of the raw material are clear disadvantages.

Hemp as an ecological alternative Hemp as an ecological alternative

Although hemp is a partly controversial plant, it can be used very flexibly. Around 97 percent of industrial hemp is processed, and for good reason: hemp is tear-resistant, diffusion-open, durable, hardly combustible (fire protection class B1), grows quickly, is not hazardous waste and has incredibly good heat and cold insulation properties. However, hemp also has a catch: an incredibly high amount of energy is needed to produce insulation material from hemp.

Flax as ecological alternative Flax as ecological alternative

Good thermal conductivity (0.040 W/(m K)), renewable raw material, open to diffusion, easy disposal and energy-saving production - when you think of ecological alternatives to building foam, there is a lot to be said for flax. Especially indoors, flax is often used for insulation, but it is not recommended for outdoor use. Furthermore, the significantly higher costs often speak against this alternative.

Chemical-free window installation: Joint tape made of virgin wool

If you want to go for pure nature, then our ISOLENA window filler is certainly a good choice. The carded wool tape can be used to insulate and fill cavities on window and door frames, as well as roof windows around the flashing. Installation is very simple: the joint tape is worked in with a spatula. Due to its high filling volume, the wool fills every cavity and insulates ideally.

"A significant advantage between the foam variant and tamping is that tamping cords (joint tape) are already available in a prefabricated form before installation. This means that a specific product can be ordered for a specific joint dimension and then installed in one or two layers depending on the joint width.

Another advantage with the joint tape made of sheep's wool is that it absorbs moisture very slowly in liquid form due to its natural lanolin content and can therefore withstand the odd driving rain - remember where sheep's wool comes from."

Helga Haslehner
ISOLENA Consulting & Sales
summarises the main advantages of the window filler

Let's look at the advantages and disadvantages in detail

  • Time factor = 1:1, compared to conventional foams.
  • No drying time, no re-cutting and rework
  • Can be applied at any temperature and humidity
  • Harmless to health
  • High sound insulation: 62 dB
  • Better fire behaviour: D-s2,d0
  • Excellent thermal conductivity: 0.033
  • Easy disposal with the best ecological balance: fully compostable
  • Advantage when reworking trades TB, soffit tapes are not damaged, a clean connection is given
  • Permanently elastic, ageing-resistant and UV-resistant

Your sheep wool insulation can be completely recycled without causing any negative environmental impact.

"Working with ISOLENA joint tape is a pleasure for several reasons.

Processing is child's play and completely harmless to health.

The technical values, such as sound values, thermal conductivity or fire behaviour, are excellent and there is no waste.

That’s why we are happy to recommend it to our customers."

Ing. Roland Dorn

Our partner from Dorn Fenster und Türen GmbH reports from the field.

Die Arbeit mit ISOLENA Fugenband macht aus mehreren Gründen Freude. Die Verarbeitung ist kinderleicht und gesundheitlich völlig unbedenklich. Die technischen Werte, wie Schallwerte, Wärmeleitfähigkeit oder Brandverhalten sind top und es entsteht kein Abfall. Daher empfehlen wir es gerne auch unseren Kundinnen und Kunden.

Ing. Roland Dorn
Dorn Fenster und Türen GmbH


PU foam definitely has its advantages. However, if you want to focus more on sustainability whilst building, there are very good alternatives available that you might not have thought of at first. Ecological alternatives can be the ideal choice for your building project. If you have any questions, please do not hesitate to contact us.