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Sponge City Mats

Water absorbing mats to keep rainwater in the city for better heat, flood and energy management.

Photo of Jurijs Kovzels
25 19

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Sponge City Mats is a way to retrofit existing rooftops to facilitate natural evaporative cooling effect. Sponge City Mats absorb and keep rainwater imitating natural environment where water is soaked up by soil and vegetation.

We all experienced how cities can be scorching hot at summer, becoming much warmer then surrounding rural areas. This phenomenon occurs in part due to unnatural way how cities manage rainwater.

In the nature, rainwater is absorbed by soil and vegetation, and when temperature rises, water evaporates producing natural cooling effect.

Unlike in natural environments, rainwater in the cities is historically dumped into pipes and drainage system breaking natural cycle and cooling.

Sponge mats are aimed to restore natural processes by absorbing rainwater and allowing it to evaporate when temperature raises.

Sponge mats is the viable alternative to reflective white roofs and green roofs.

White roofs are found to be effective in reflecting sunlight and cool down the surface of the roof. Sponge mats when painted with reflective white coating provide the same benefits, and besides that, leverage evaporative cooling effect.  

Green roofs, roofs with soil and vegetation, provide benefits of natural cooling but entails high installation and maintenance cost and can be inefficient in water deprived regions.

Sponge mats leverage benefits of both white and green roofs and is cost-efficient and low-maintenance solution.  

Sponge mats are produced of 99% percent on recycled Nike Grind materials.
Sponge mats leverages inherent properties on Nike Grind materials to absorb and keep water and requires close to zero energy consumption to build.

Website (if applicable)

Which Nike Grind materials will your idea utilize?

  • Rubber Flashings
  • EVA Foam Injection Scraps
  • EVA Foam Flashings
  • EVA Foam Components
  • Laminated EVA Foam
  • Laminated PU Foam
  • Mixed Footwear Textile
  • Split Leather Scraps Coated

How specifically will these materials be incorporated into your solution?

The Mat consists of 2 main layers: absorption and isolation layers. Spongy absorbing layer, composed of the mix of Nige Grind materials. Composition of the materials and methods to fasted or clue the grind will be determined experimentally to achieve best absorbing and evaporating properties. Thin liquid rubber waterproof isolation layer covering the mat all sided except the top to form a container holding rainwater. This layer is optional. In the long run melted foam and rubber Nike Grind materials can be used fasten the component of Absorbing layer and to form outer isolation layer. This will make the entire production of the mats use only recycled materials.

What is the current stage of development of your idea?

  • Research & Early Testing

Describe your target market. Who will benefit from your product?

Primary application: 1. Factories, warehouses, or any number businesses operating from flat roof buildings and spending money on air conditioning of premises. 2. Residential communities making building more energy efficient and improving living conditions. 3. Walkable modification can be used in public spaces and on playgrounds. Alternative applications: 1. Sealed in fabric can be used to alter soil mechanics in landscaping and agriculture 2. Office workers when used as acoustic panels

How will you scale your idea? Please describe in detail your plan to scale your concept.

Berlin is the optimal places to start and scale business like Sponge Mats. Germans are ecologically conscious and willing to make sacrifices in the name of energy independence and climate protection. Business are pushed to improve energy efficiency due to the costs and governmental requirements. Thriving social entrepreneurship startup scene. We will seek partnerships with local businesses through governmental organizations and social impact communities. We will also reach and work together with city architects to improve the design and incorporate the mats into upcoming city improvement projects. The core concept of the mats has multiple applications and allows leeway to adjust and pivot the business model. The biggest challenge to deliver the product to market is navigation of German fire safety and construction regulations with can be tricky and time consuming. To mitigate this challenge, we will start dialog with authorities at the early stage of the project development.

How is your idea innovative?

Sponge Mats utilize recycled materials in the new way allowing to imitate natural process making city ecosystem better for living and more environmentally friendly.

What inspired this idea?

Idea of Sponge City is nothing new. Berlin's suburb Rummelsburg, build 20 years ago, is an example of this concept. The problem is that it is not feasible to rebuild existing cities to handle water more naturally. Sponge City Mats can help retrofit some existing building and city surfaces.

Tell us about yourself and your team. What is your background and experience?

Jurijs is Service Designer with entrepreneurial experience. Jurijs is interested urban development, mobility, and sustainability. Mariia is Marketing Expert with Business administration and economics education and experience in B2B sales.

In what city are you located?


In what country are you located?


Please describe how becoming a Top Idea will support the growth of your concept.

Funds will allow as develop and deploy first prototypes for testing and iterate on the design. Part of the funds will be used to test different marketing channels and developing marketing materials.


Join the conversation:

Photo of Avneesh Panwar

Thanks for this post

Photo of Adriana Sarocco

I love this idea.
I think it is a good idea to start with Berlin- a city that is very focused on sustainability and is, relative to other cities of the world, far along in green efforts. Each city I think would need it's own customized sponge city solution- and I think it would start with looking at the soil make up of the surrounding area. Nature is the ultimate designer - so it would be interesting to try to mimic the layers of soil found in nature with the materials used in the city. I would think in a city like San Francisco, there may be some issue of how the material would stand to common natural disasters , like earthquakes or fires. As climate change progresses- we see more intense and frequent natural disasters- I think it would be interesting to explore if this material be something that you could pitch to local government to be a better alternative to current materials due to potential $$ saved.

In the spirit of circular innovation- it would also be interesting to explore if there is a way to loop water collected back into homes or perhaps to city gardens to further the sustainability concept.

Photo of Aaron

Cool idea

Photo of Linda jack

Grains are so important and it play an important role in our lives and so many people are using them in their daily life. You may also know about the assignment website you will be known about the so many products and about their prices.

Photo of 瑞康 黄

I had never seen such a good idea about Nike Grind materials. Other people’s may heard amazing but only the data can persuade the company. In your idea you said that "Sponge mats are produced of 99% percent on recycled Nike Grind materials.” It is amazing taht if you can do it.

Photo of Rupert

Interesting idea & based on a proven principle.
It would certainly use a considerable quantity of Grind material too.
I'm assuming that a natural partner would be one interested in using your mats as a host for rooftop agriculture.
There is a potential issue in the sheer mass of the mats on a large flat roof once hydrated, which might limit use on factories and warehouses which tend to be built cheaply with large spans.

Photo of Lauren Ito

hi Jurijs Kovzels ,

A reminder that the ideas phase of this Challenge closes in less than one hour, at 5:00 p.m. Pacific Time. Please have your submission updated by this deadline with content to all proposal questions complete.

Excited to have you in the Challenge!

Photo of Dylan Bochsler

Hi Jurijs Kovzels ,

Very cool idea, and it seems to be a pretty well developed concept.

Here in Oregon, we get a lot of rain, so my #1 concern would be whether these mats will retain too much water, or if you plan on having them drain into conventional roof drains?

If you did plan on having them retain water, do you know how much? At roughly 8lbs per gallon, you can add a lot of weight in a hurry on a large roof - which may or may not be structurally sound enough to handle this. Just a thought!


Photo of Clélie

What a wonderful idea! This “sponge city” concept is really inspiring!

Would your solution be suitable for pitched roofs or do you only target flat roofs? I know that some companies have found solution for green roof with a slope of up to 60%; but it required innovation to avoid an accumulation of water in a given place, and to distribute the weight correctly.

Moreover, green roofs ensure a high level of water absorption thanks to the plant itself. The remaining water is released into the air by evaporation, or released into the pipes with a delay time. In the absence of plants, does it mean that the roof is less efficient and absorb less water?

Excited to learn more about your company and product!

Photo of Awen Delaval

Hi Jurijs;

I like your idea to create absorbent mat.
However, by using Nike grind only, I am scare that your map wouldn't be absorbent but waterproof eventually.
I would suggest to add a natural microfiber which will make your material absorbent and fast drying.
Should you need more information, d not hesitate to contact me,

Photo of Lauren Ito

Hi @Jurijs Kovzels and @Mariia Shekhireva ,I hope you had the chance to attend the prototyping event! With less than two weeks left in the Challenge, I want to make sure your submission is set up for success by the deadline for completion! To help us visualize what your mats might look like, feel like, how they might be installed, etc. can you upload sketches of the product journey from raw materials to installation?Also including this rapid prototyping resource which may be helpful to guide your process:

Photo of Tim


I like the idea, but I see a possible draw back with current design; that without the ablity to drain the sponge or allow air to pass through it, it may become a breeding ground for bacteria, possible even legionaries disease. This would probably worse during damp and cool periods but during the winter the sponge could just freeze into a block ultimately destroying it's structure. You mention that sponges have already been used for this purpose so it may be worth investigating if they were free draining and if not whether my fears materialised.

Whilst your current design may have problems in temperate climates, it could work quite well in the tropics providing cooling by water evaporation. The mats could sit on flat roofs, a common feature of many structures in this region, being feed or sprayed with water.

One other point, as I understand it vulcanised rubber is very difficult if not impossible to reshape or remould, hence it inclusion as granulate in this challenge. And I suspect that none of the other materials on the list can be readily made to act as an adhesive so it may be worth considering non recycled materials for this function.

I hope these criticisms are constructive.



Photo of Tim

An additional thought, water from a free draining sponge could be collected in a water butt or other storage container to be returned by a pump (solar) when it is best required. This would address the issue of excessive roof loading and allow the sponge to provide insulation in the winter and cooling in the summer.

Photo of Jurijs Kovzels

Hi Tim!
Thanks for the idea, I think it will be a great addition for the efficiency of the solution.

Photo of Naman Mandhan

Hi Jurijs Kovzels !

Fantastic idea! It's amazing to see all of the incredible work being done in Germany around this incredible concept of a "sponge city".

I'm curious about how the buildings might be retrofitted with these mats? Could you provide more details on what that might look like, in terms of key partners involved, the process of carrying out these retrofits, and any potential changes that will need to happen to the infrastructure. Has your team been able to speak with any city planners/urban designers/civil engineers and received feedback?

Do you envision these mats to be a 1:1 replacement for soil and vegetation in terms of absorbing water, or would this need to be some sort of hybrid between extremes? Tagging in Alexandra Ralevski to add thoughts and ideas from her experience working in biomimicry.

Excited to see this concept develop and hear your thoughts!

Photo of Alexandra Ralevski

Hi Naman Mandhan and Jurijs Kovzels,

Interesting idea. Current “sponge cities” use "natural" sponges such as greenery, rain gardens, or bioswales. Using these has multiple benefits, the main one being longevity. They are oftentimes self-maintaining, and can last for several decades. Additionally, having green spaces around a city has been shown to have multiple health benefits.

For your sponge city mats, I believe you will need to show that they are either more beneficial than using “natural” sponges, or that your mats can be used in places where greening a space is not an option.

Three main points to consider:
1) Which materials will be in your absorbing layer? What is their permeability/absorbency rate?
2) Make sure the product won’t leech chemicals (EVA, glues, etc) back into the water after absorbing.
3) What is the longevity of the mats? Can they handle multiple rounds of soaking and drying for decades, or will they need to be replaced after only a few cycles? Can the material be recycled again after?

I should also mention that this isn’t biomimicry per se, as is it’s simply attempting to copy something nature does, but not how it does it. If you want to improve your design, look into examples of how nature absorbs/evaporates water so well (using different materials, layers of different sized materials, etc).

Let me know if you have any questions.


Photo of Jurijs Kovzels

Hi Naman Mandhan 

Thanks for your question.

We think that individual roofs can be retrofitted with a small team of construction workers/roofers. We also see the necessity to have someone with architectural education and knowledge in the team to ensure compliance with regulations, take measures and make estimates. It is also possible that mats can be made-to-measure in field conditions, directly on the roof, driving the operation costs down.
At this moment we are reviewing regulations and materials available for the subject and planning on contacting experts and authorities later.
As for replacing soil and vegetation, no, this is not the goal. We believe that mats or Grind materials in general can be applied for hear, water and energy management in cases when other approached are not viable for one reason or another. Mats can find a niche in between white roofs and green roofs.

Thanks for referencing Alexandra Ralevski , we are excited to hear her opinion!

Photo of Jurijs Kovzels

Alexandra Ralevski  – thank you for your feedback and deep insights.
I completely agree greenery is much better option then rubbery mats. I do not think, and frankly hope, that this solution could ever replace natural sponges (soil and vegetation). Nevertheless, there might be a niche for mats where vegetation is not viable, areas with severe long-lasting droughts, decked or paved roofs and surfaces, roofs with low max weight limitations (e.g. metal hangars and warehouses).
I am interested to know if you think those examples are reasonable and if you have other examples where greening a space is not an option?

Thanks for listing points to consider. Those are the questions to be answered. Next week we are attending an event organized by Nike and OpenIDEO in Berlin – we hope to get some answers there.

One thing we are struggling with is understanding if it is a good idea to combine Grind and soil? For example, using grind as an alternative to LECA a.k.a hydroponic balls ( as it is used in agriculture and gardening.

Photo of Alexandra Ralevski

Hi Jurijs Kovzels ,

Those seem like good options. I would also suggest areas like driveways, parking lots, or even basements in areas that are prone to flooding. With regards to combining Grind materials with soil, they may end up serving a similar function as perlite/vermiculite, rather than the clay aggregate you mentioned. Which specific Grind materials were you thinking of?

I would also encourage you to think about WHY green spaces are so good at absorbing water. One way is by using layers of different materials to serve different functions. Additionally, green spaces erode less quickly than man-made products. Here is a link to a case study Biomimicry 3.8 did for a client working in a monsoon-heavy area, with a pdf link at the bottom:

In the pdf you see that in monsoon-heavy areas (with up to 27 feet of rainfall), leaves in the canopy above the forest floor help to dissipate the energy of the falling water droplets, leading to less erosion. This also helps to slow the total amount of water that's absorbed at one time.

Have fun at the Nike event in Berlin!


Photo of Lauren Ito

HI Jurijs Kovzels ,

Great to see you in the Challenge. To understand more about how you might utilize the materials you've selected in your final product, could you please provide a paragraph or two to the question "How specifically will these materials be incorporated into your solution?" It may be helpful to do some research on how current these mats are currently processed and see how these materials may be used/substituted in that process as a starting point.

I'm also tagging in Challenge community rockstars, Robert Smith , Naman Mandhan , and Aakar Mehra . I encourage you to provide feedback/questions on one another's concepts to accelerate the design and innovation process!

Excited to learn more.

Photo of Jurijs Kovzels

Hi Lauren Ito Thanks for bringing people and opinions to this idea. We will be updating over the next few days the descriptions of the idea. Stay tuned!

Photo of Dennis Lejardi

Hi all!

Jurijs Kovzels This is a fantastic idea! There are a number of directions or add-on benefits we can retrofit this project with. Keeping the SpongeMat City idea intact, if we remove the insulation layer on the bottom portion of the structure you can lead water to be permeate to the bottom to be collected. Collected rainwater can be stored to be utilized and/or filtered for toilet flushes, sinks, showers, etc. In this regard, we have created insulation, a water collection system, and a structural element to a building.

Naman Mandhan Rubber has been used as an aggregate for concrete previously and if used as a non-fine aggregate - this can allow for water to permeate through at a quicker rate than some other concretes. In regards to 1:1 replacement for soil/vegetation, I'm not an expert on soil qualities, but I would assume this would have to depend on the quality of the soil in the region that you intend to build upon and what may be the best approach. Worst case scenario might be a setting where you have an impermeable and unstable soil base to build off of. This would be a two fold problem - Permeability of a soil works in favor of this design seeing as it allows excess water that does not dry up to be absorbed. A solution may be to create channels from the building leading the water to an appropriate release area. Instability in the soil has many ways to be dealt with, so again the solution to this would depend on the type of soil in the area.

As a non-fine concrete aggregate, a "rubber mat" style application can be utilized in road infrastructure and applied on runways, sidewalks, streets, drive-ways and more! I'm picturing a design similar to Permeable Concrete, which allows water to permeate through the solution at an incredibly quick rate given the right soil conditions. In areas/environments where heavy rain may be a relatively common condition, incorporating this into certain strategic locations of its infrastructure may make roads and walkways safer for drivers and pedestrians, while also reducing flood damage risk to areas that may be at risk.

I'd love to hear any thoughts on some of these suggestions or ways to improve these approaches!

Photo of Jurijs Kovzels

Hi Dennis Lejardi !
Thanks for kind words, and thanks for references to Permeable Concrete and no-fine aggregates. I need to look into it.

Removing insulation/isolation layer is something we think about as well, but this decision depends on properties on materials or mix of materials. Foam will hold some water while rubber will not. At the same time, we can vary the height of the mat allow water to drain when the mat is full.

Photo of Aakar Mehra

Hi Jurijs Kovzels and Mariia Shekhireva ,
That for sharing this idea with us! The overall concept of the "sponge-city" is really amazing. I spent about 30-40 mins reading and watching videos on it.
You bring up good concerns about scaling the product with permission of the city government. Another problem that I can think of is, what if the water absorbing material does not dry up for a few days (maybe due to cloudy weather)? The grind material (foam and EVA), will probably start to get some mold (fungus) on them. I could be wrong, but I have seen this on my old shoes. I think it is easy to do a quick test on this with a pair of old shoes, just soak them in water for a while and make sure they don't dry for a few week.
Currently in Berlin, it seems like they mostly use grass and soil to soak the water, which can process it into growing plants. I think if you can build a design (simple sketches) where we can start using some of this water into plantations or something, that would be great!

Looking to see sponge-cities being made across the world!

Photo of Jurijs Kovzels

Hi Aakar Mehra , thanks for your questions!

Regarding city permission, we are gathering some insights as I'm writing it. Default load-bearing threshold for flat roofs is 250 - 500 kg/m3, so the additional load should not be a problem.

Mold and mildew most definitely will grow on mats without special coating or paint. It also may be the case that mats will grow moss, which might actually give additional benefits.
Mats can become a low-cost, low-maintenance urban heat island mitigation technique [1]. By no means it will replace existing techniques such as green roofs and white roofs - rather a piece of the puzzle to make the city a better place for living.

As we see it now there are many options and possibilities. Mats can be 5 to 10 centimeters tall, they can have or not have isolation layer (when the roof is water-proofed itself). They can be walkable or one can install decking on top. They can be painted white to reflect the sun light or can accommodate solar panels. Some of the suggestions will be proven wrong on prototyping phase, and many more ideas and variables may occur, but fundamentally we believe that Nike Grind can be used to keep rain water in the city, instead of dumping it to the sewage system.

We will be updating the descriptions of the idea, stay tuned!