October 4, 2025

Our Journey to Reinvent the Sandbag

When we first learned that archaeologists often face landslides at excavation sites, we wondered: What if sandbags could be light to carry, expand on demand, and be reused responsibly?

That question became the heart of our FIRST LEGO League Innovation Project — and it sent us on a journey filled with science, creativity, and real-world problem-solving. Today, we met with a polymer expert who helped us take our idea from a fun prototype toward something that could actually work in the field.

The Problem We’re Tackling

At archaeological sites, rain and runoff can quickly erode trenches and damage fragile artifacts. Traditional sandbags do a good job protecting these areas, but they’re heavy to move, slow to deploy, and difficult to reuse once they’re full of wet sand.

We wanted to change that. Our goal was to design a lightweight, multi-use bag that starts small, expands when wet, and can be dried and used again.

To make that possible, we explored sodium polyacrylate — a super-absorbent polymer that’s also found in baby diapers. It can soak up hundreds of times its weight in water, which made it a perfect candidate for our concept.

What We Learned From a Polymer Expert

To make sure our idea made scientific sense, we met with Dr. Shunzhi Wei, a polymer researcher. Her insights helped us understand what parts of our design were on the right track — and where we needed to keep experimenting.

We learned that sodium polyacrylate is a strong starting material. It’s affordable, easy to find, and extremely good at absorbing water — ideal for early prototypes.

Dr. Wei also explained that the outer layer of the bag must stretch. Because the polymer expands so much when it absorbs water, the outside can’t be rigid or stiff. Instead, it should be flexible and “balloon-like,” made from rubbery or elastic material that allows safe expansion.

We also discovered that reusing the polymer is possible but not simple. Once the polymer is wet, drying it out takes time and energy. It can be pressed, spun (like in a washing machine), or left in the sun, but each method has trade-offs in effort and speed.

Finally, Dr. Wei reminded us that safety and disposal are part of engineering. Sodium polyacrylate is generally safe to touch, but it shouldn’t be eaten or get in your eyes. And when used in larger quantities, it must be disposed of properly according to safety guidelines.

These lessons helped us think more like real engineers — balancing creativity with responsibility.

Our Prototyping Journey

So far, we’ve tested three different filling materials: super-absorbent polymer, wood chips, and paper chips. The polymer performed the best, so that’s where we’re focusing our next round of testing.

Right now, we’re working on four main areas of improvement.

First, we’re designing smarter outer shells. We’re testing materials like canvas, synthetics, and rubberized fabrics to find something lightweight yet flexible enough to expand and contract without tearing.

Second, we’re studying drying and reusing methods. We’re experimenting with three approaches:

1. Compression — squeezing water out with a press or wringer.

2. Centrifugal force — spinning out water using baskets or mop-bucket spinners.

3. Passive solar drying — laying the bags out in the sun.
   
   

For each method, we’re measuring drying time, how much weight the bag loses, and whether it stays strong across multiple uses.

Third, we’re testing containment and safety improvements. We’re exploring “encapsulated” absorbents (like Orbeez-style beads) to prevent fine particles from escaping during use or drying.

Finally, we’re focused on tracking progress carefully. Every prototype is labeled with its contents, weight, and number of test cycles — because in engineering, data tells the story.

The Road Ahead

In the coming weeks, we plan to keep improving our design. We’ll compare different shell materials for strength and flexibility, measure drying times across our three reuse methods, and test bead-based polymers for better containment.

We’ll also build simple demos to show how our sandbags expand, stack, and dry — and create visuals and scripts that explain our safety and environmental practices.

Each test gets us closer to turning an idea into a real, reliable solution — one that could help protect archaeological sites, and maybe even other flood-prone areas, in a more sustainable way.