Cut the 1.5 litre bottle in half, 17cm from its base.
Decorate the inside of the bottle with markers and shapes cut out of self-adhesive plastic sheets.
Wrap a sheet of aluminium foil around the glass bottle with the shiny side against the glass. Press down so that the foil takes the shape of the bottle.
Fill the base of the PET bottle with isolaiton at a height of about 3 cm.
Insert the glass bottle in the center leaving under it's bottom about 2cm of insulation.
Complete the insulation around the glass bottle up to about 1cm from its neck (if polystyrene beads are used, finish with some wool to prevent the beads from escaping).
Blow the top of the PET bottle with a hot air gun to 'retract' it onto the neck of the glass bottle. Quickly, squeeze the top on the PET bottle so that it follows the shape of the glass bottle.
Surround the top of the PET bottle with adhesive tape.
Cut the 1 litre PET bottle in half at 11 cm from its bottom. Check that the cup fits into the PET bottle section. Decorate the inside and then add insulation (e.g. wool, hemp, etc.) forming a 'nest'. Place the cup in this 'nest' and complete the insulation around it.
Blow the top to 'squeeze' the PET bottle on the cup.
Cover the edge of the bottle with thick adhesive tape to secure and seal both elements.