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Expanding Foam Vs. Concrete Fence Post: Which Is Better?

Concrete has been out there for a while now. If we take the many forms of concrete into account, we can certainly say that they have been around for more than thousands of years now. We first saw the modern version of it in the mid-1820.

The material known as concrete is inexpensive and yet one of the most durable materials out there. Then we have the expanding foam, which has been around since the 1950s.

However, since we are talking about the post hole filler expanding foam, then we have to mention that this is rather new a product.

Today we have taken quite a bit of time and looked at both of their differences, uses, and properties to give you a definitive answer as to which one of them is better. Better in the aspect of post hole filling, let us keep reading to find out more.

Expanding Foam vs. Concrete Fence Post: Which Is Better?

Usually, it is concrete that gives strong support for these types of products. Expanded foam or materials similar to that does not even come close to the rigidity and the density of concrete. The expanded foam post is relatively strong to keep the post up in normal circumstances.

We first need to understand how much consistency of a product like these matters when we are comparing them.

We are comparing expanding foam against concrete to find which one is better. On the other hand, their consistency of them is drastically different from each other.

Concrete is a tough rigid material while expanding foam is a lightweight material. The whole point of fencing is to keep the border up as well as keep things out. Not just keep things out, they also help in keeping the things that are in safe as well.

Therefore, it is rather crucial for a material that would be used as filling for the post, needs to be sturdy.

This is where the expanding foam lacks the most behind. The foam is a lightweight material that does the job of a concrete post fence material half-heartedly.

Concrete is the heavyweight here due to the price difference for the same amount of material for post fence hole filling.

However, there are times when the expanding foam is better, but those cases are all temporary and only concrete can give you a permanent solution.

Expanding foam has the quality of being very easy to use and fast processing of the product. It can take around 1 min to an hour only for it to cure and all that without using water. Concrete on the other hand can take up to 30 days to cure.

What is expanding foam?

Expanding foam is made up of two different materials. These materials are isocyanate and polyol resin. The foam has no required weather for its usability. We can use the expanding foam in any type of weather both hot or cold.

The expanding foam is also lightweight and waterproof, making it a great alternative to rigid concrete material. When this material mixes this can expand 30-60 times its original liquid volume.

However, this new material with all its pros has a few cons to it, most notably the price tag on this product is very high. In comparison, there are many materials out there with similar attributes and a lower to zero price tag depending on certain situations.

When we use the expanding foam, we do not need any water or other types of liquid to go with the mixing process.

Is expanding foam as strong as concrete fence posts?

When it comes to concrete can withstand some of the harshest environmental events. However, the expanding foam only has enough toughness to withstand mild environmental events.

Concrete’s consistency is much denser than that of the expanding foam. While the expanding foam has a less supportive consistency. The difference inconsistency between the two materials is rather large.

So, to answer the question, no, expanding foam is nowhere near as strong as concrete fence posts. They are not as rigid and supportive as the concrete post. Concrete wins this argument with a landslide.

Even though concrete wins in harsh environments, it does not however mean that the expanded foam is rather useless. There are many uses of this unique material that can get tough when the going gets tough.

What is the difference between expanding foam and concrete fence posts?

The expanding foam is a modern solution that most of us casual people can use without any hassle or making a mess. Concrete fence posts are a job for the permanent folks out there providing a commitment to their work and spending countless hours making it.

There is a clear and definitive difference between the two products. We are going to go into more details about those as well as other differences between them.


Expanding foam is a lightweight alternative to the fence posts. The concrete on the other hand is much harder and heavier than most other fence post materials.

Therefore, in this case, concrete is better due to how rigid and sturdy it is.


Concrete in comparison costs less than polyurethane foam which is much lighter than concrete. If we were to find the difference in cost the cost would be three times the cost of an equivalent amount of concrete.


Concrete takes a huge amount of time to cure, for example, it would take it somewhere from 7 to 30 days sometimes. However, for the expanding foam, it only takes from 1 min to 1-hour max to cure.


A lot of the common fence repair materials and spikes can be used on the concrete posts easily and support these and other products as well. However, there are a few little repair tools for the expanding foam.

Can you use expanding foam for fence posts? What can I use instead of concrete for fence posts?

Of course, you can use expanding foam for fence posts. Expanding foam is a lightweight contender to the concrete material which can be the heavyweight champion among the two.

However, due to the qualities of expanding foam, many people just go for it over the concrete.

The foam can be used without mixing water or using any type of other liquid. Hot or cold weather does not matter which it is, you can still use the expanding foam little to anyone’s surprise.

Furthermore, there are a few other things you can use instead of concrete, such as


We can easily use dirt for fence posting. This is usually the simplest solution for a fast and efficient temporary fence posting. If we are to follow the correct process the fence will be pretty strong in comparison.


Then we have gravel, which also can be a great alternative to concrete. It requires no preparation or planning. Furthermore, it helps with any drainage problems both underground or around the base.

Crushed Rock:

We can use crushed rock when we set fence posts as well. This is a rigid solution instead of concrete and we can DIY it very easily. We have all used crushed rock somewhere at any point in our lives.

How to set a fence post with expanding foam?

Depending on the standard brand of expanding foam below is the usual way to set a fence post with expanding foam.

  • Dig a hole with the help of a shovel.
  • Set the post in the center of the hole and ensure that it’s upright.
  • Using plastic gloves layout the resin and follow the instructions of the manufacturer for mixing the resin.
  • To create the expanding foam, we have to get each bag that contains the two resins. Follow the instructions and mix them appropriately.
  • When the bag turns yellowish-tan color, we cut off the corner of the bag and squeeze the foam out of that corner.
  • We apply the foam around the post and let it cure for an hour.

Final Thoughts 

Expanding foam and concrete fences both are good contenders when it comes to posting fence materials. However, both have different cons and pros. The pros for a good secure fence post material lean more toward the concrete one than expanding foam. Thus, we can say concrete is the better option.