The balloon envelopes used in the project are made by Raven Aerostar, and are composed of polyethylene plastic about 0.076 mm (0.0030 in) thick. The balloons are superpressure balloons filled with helium, standing 15 m (49 ft) across and 12 m (39 ft) tall when fully inflated.
They carry a custom air pump system dubbed the "Croce" that pumps in or releases air to ballast the balloon and control its elevation. A small box weighing 10 kg (22 lb) containing each balloon's electronic equipment hangs underneath the inflated envelope. This box contains circuit boards that control the system, radio antennas and a Ubiquiti Networks 'Rocket M2' to communicate with other balloons and with Internet antennas on the ground, and batteries to store solar power so the balloons can operate during the night.
Each balloon's electronics are powered by an array of solar panels that sit between the envelope and the hardware. In full sun, the panels produce 100 watts of power, which is sufficient to keep the unit running while also charging a battery for use at night. A parachute attached to the top of the envelope allows for a controlled descent and landing when a balloon is ready to be taken out of service.
In the case of an unexpected failure, the parachute deploys automatically. When taken out of service, the balloon is guided to an easily reached location, and the helium is vented into the atmosphere. The balloons typically have a maximum life of about 100 days, although Google claims that its tweaked design can enable them to stay aloft for closer to 200 days.
He prototype ground stations use a Ubiquiti Networks 'Rocket M5' radio and a custom patch antenna to connect to the balloons at a height of 20 km (12 mi). Some reports have called Google's project the Google Balloon Internet.
The balloons are equipped with automatic dependent surveillance – broadcast and so can be publicly tracked (along with other balloons) with the call-sign "HBAL"