Please don't leave balloons in a hot car - helium expands in the heat and this could cause your balloons to pop! We recommend that you use air conditioning in your vehicle when transporting balloons on a hot day. If balloons get rained on and start to droop, don't worry – they'll float again when dry. When helium-filled balloons are taken into the cold, they will temporarily deflate and will re-inflate again when warm. A change in temperature (going from warm to cold) can cause a vinyl personalised message on your balloon to bubble slightly.