Are Compostable Bags Actually Compostable? The Science Explained

Compostable bags are marketed as an eco-friendly alternative to traditional plastic, but many consumers still wonder: Are compostable bags actually compostable, or is it just green marketing? In this SEO-optimized, research-based guide, we break down the real science behind compostable bags, how they work, and whether they truly help the environment.

What Are Compostable Bags?

Compostable bags are made from plant-based, renewable materials rather than petroleum-based plastics. Common raw materials include:

• Cornstarch (PLA – Polylactic Acid)

• Sugarcane fibers

• Potato starch

• PBAT (a compostable biopolymer)

Unlike regular plastic, compostable bags are designed to break down into natural, non-toxic components under controlled composting conditions.

The Science Behind Compostable Bags

Compostable materials degrade through microbial activity, heat, oxygen, and moisture. This process converts the material into:

• Carbon dioxide (CO₂)

• Water (H₂O)

• Biomass (nutrient-rich compost)

For a bag to be truly compostable, it must meet strict scientific standards such as:

• ASTM D6400 (USA)

• EN 13432 (Europe)

• OK Compost Home / Industrial

These certifications ensure the bag breaks down within a specific time frame and leaves no toxic residue.

Compostable vs Biodegradable: The Real Difference

Many people confuse these two terms, but they are not the same.

Key fact: All compostable bags are biodegradable, but not all biodegradable bags are compostable.

Do Compostable Bags Break Down in Landfills?

Here’s the scientific truth:

❌ Compostable bags do NOT compost properly in landfills.

Landfills are usually:

• Low oxygen

• Low microbial activity

• Dry or sealed environments

Without oxygen and heat, the microbial composting process can’t occur. This means compostable bags behave much like traditional plastic when disposed of in regular trash.

However, they are still a better environmental option than petroleum plastic because they are made from renewable materials and don’t release toxic microplastics.

How to Make Compostable Bags Actually Compost

To ensure compostable bags break down properly, they must be disposed of correctly.

Best Composting Options:

✅ 1. Industrial Composting Facilities

These facilities provide:

• High heat (above 55°C / 131°F)

• Oxygen flow

• Moisture control

Most certified compostable bags are designed specifically for industrial composting environments.

✅ 2. Home Composting (Only If Certified)

Only bags labeled “OK Compost Home” are safe for backyard composting systems.

⚠️ Note: Dog waste should NOT be added to garden compost used for food plants.

Environmental Benefits of Compostable Bags

Despite limitations, compostable bags still offer major advantages:

• Reduced fossil fuel dependency

• Lower carbon footprint

• No long-term microplastic pollution

• Safer for marine and land wildlife

Switching to compostable bags is an easy step toward sustainable living.

Common Myths About Compostable Bags

❌ Myth 1: Compostable Bags Break Down Anywhere

Truth: They require specific composting conditions.

❌ Myth 2: They Compost in Your Kitchen Bin

Truth: Most kitchen compost bins are not hot enough.

❌ Myth 3: Compostable Bags Are Just Greenwashing

Truth: Certified bags meet strict international scientific standards.

Are Compostable Bags Worth It?

✅ Yes — When Used Correctly

They are one of the most responsible alternatives to plastic, especially when paired with proper composting practices. While not perfect, they significantly reduce environmental harm compared to traditional single-use plastics.

Final Verdict: Are Compostable Bags Actually Compostable?

Yes — compostable bags are genuinely compostable under the right scientific conditions.

They require:

• Oxygen

• Heat

• Microbial activity

• Proper composting facilities

When disposed of correctly, they break down efficiently and safely, making them one of the best eco-friendly packaging solutions available today.