Make homemade hot air balloons

Before you begin

• Use the safety checklist to help you plan and risk assess your activity. Take a look at our guidance to help you carry out your risk assessment, including examples. 
• Make sure all young people and adults involved in the activity know how to take part safely.
• Make sure you’ll have enough adult helpers. You may need some parents and carers to help. 

• Plan to run this activity indoors to prevent plastic pollution, and prepare a collection point for all materials to be reused or recycled after the activity.
• Bin bags used should be biodegradable or recycled plastic bags, encourage reusing people might already have at home instead of buying new ones.
• You could bring in a range of recycled or biodegradable materials to see which works best. Such as: lightweight fabric, tissue paper, compostable bags, reusable shopping bags, or packaging film. 

Creating bin bag hot air balloons

1. Divide participants into small groups. Explain you’ll be making hot air balloons using bin bags and recycled materials.
2. First, each group should take a bin bag and tie the handles together.
3. One person in each group should take the bin bag and, holding the bag by the handles, wave it from side to side or around so it fills with air.
4. Once it's filled with air, turn the bag upside down, so the handles are pointing towards the ground, and let go. The bag will likely float down to the ground.
5. Each group should talk about what happened and why they think it happened.
6. The bag sunk because the air inside it is cold. Cold air is heavy, so the bag sinks.

Launch the bin bag hot air balloons

1. Now, each group should take a black bin bag, cardboard tube (such as an empty toilet paper roll) and a hairdryer. You may need extension leads, depending on where your plug sockets are.
2. Tie the bin bag handles together, so that only a small opening remains and tuck the handles inside so they’re not loose. This is like the balloon of a hot air balloon. 
3. With adult supervision, slide a cardboard tube into the bag opening. This'll make it easier to fill the bags with air and it'll also reduce the risk of the bags melting. This is like the skirt or throat of a hot air balloon. 
4. With adult supervision, while someone holds the bags using the hairdryer on the coolest setting, one person from each group should slowly fill the bin bag with air. The cool setting will still create warm air, but won’t melt the bags. This is like the burner of a hot air balloon. 
5. As they fill with warm air, they bin bags should start to float and eventually fly away. As the air inside them cools, they'll sink back down to the ground. 
6. Let each person have a go and see how high they can get the plastic bag hot air balloon to fly.

How it works

1. Ask everyone why the bag floated with the warm air, but not the cold air.
2. Explain that warm air is lighter than cold air because the air particles are spread out. When you blow hot air into the bag, the air inside is lighter than the air around it, so the bag rises.