Is loft insulation fibre good at keeping in the heat?

Listen to and watch the video.

Get two identical glass bottles (ketchup bottles, for example). You also need some insulation roll - just a little, perhaps a few tens of centimetres. You may find you have some left over at home.

Fill both with hot (not boiling) water and use a thermometer to measure the temperatures in each bottle. Now wrap one of the bottles in insulation fibre. Measure the temperatures again after an hour. Which one would you expect to show a higher temperature? How long does it take for the insulated water to cool down. Remeasure the water every hour to find out.

Now try to give reasons for each of the things you have seen.