Monster Birthday Round Foil Balloon 18″. Let googly-eyed creatures welcome guests to your next big bash with this fun foil Monster birthday balloon. Featuring colourful aliens and “Monster birthday” text, this foil balloon is sure to delight kids at a Monster themed party. Tie this balloon outside to the gatepost so friends can easily spot the right house for the celebration, or try combining it with latex balloons to make a lovely balloon bouquet to use as a table centrepiece.