ROME  - Ten teams of young international designers battled it out to produce an innovative eco-friendly popemobile that could guarantee high "Pope visibility," meet strict security standards and promise low emissions.

Some proposed features included sunroof panels that would open like flower petals to side windows that could "live Tweet" messages to and from the pope.

The winners, however, kept it simple.

Eric Leong, 24, of Toronto, and Han Yong-fei, 23, of France, modified a hybrid Volkswagen Cross Coupe concept car into a white popemobile with an expandable solar roof and bullet-proof wheels. Their design also featured so-called "spray-on battery" technology in which each element of a traditional lithium-ion battery is incorporated into a liquid that can be sprayed, in layers, on many kinds of surfaces. The spray-on technology provides "better efficiency" for rechargeable batteries by reducing the car's weight, the designers said.

One eco-popemobile design finalist was a team of students from Turin's European Institute of Design. They used a BMW ActiveHybrid X6 vehicle and gave it a back roof made up of two dozen folding panels that could open up like flower petals, allowing the Pope to stand and greet the faithful. The car design also featured armoured side windows that double as monitors capable of displaying live, "selected Tweets for and from the Holy Father," according to the young design makers.

The Italian car-parts manufacturer, Berman, sponsored the competition near Mantua, Italy, Oct. 11-12 and invited select car design students from around the world to submit their drawings.

It marked the first time the annual Autostyle Design Competition had a special category for a popemobile, according to L'Osservatore Romano, the Vatican newspaper.

A panel of judges, including design directors from Alfa Romeo, Audi, Bentley, Fiat, Ford, Ferrari, Toyota and the University of Florence, picked the winning designs "based on their consistency with (a major carmaker's) brand, their originality and innovation, the comprehensiveness and elegance of the work and the feasibility of the projects," according to cardesignnews.com.

The popemobile designs had to use a production hybrid car model or concept car design and keep the car model's front features so as to maintain the brand image. Only the rear of the vehicle could be modified and it had to be done in such a way that it guaranteed comfort for five passengers and maximum "visibility of the Holy Father," it said.

Projects needed to use alternative energy, cutting-edge materials and innovative technology that allowed for rapid and easy rear access to and from the vehicle.

The Volkswagen Cross Coupe concept car uses two electric motors and a next-generation turbo diesel engine, according to manufacturers.

The Vatican publishing house, LEV, will publish a volume of the competition's best "green" popemobile projects and designs.

Pope Benedict XVI has frequently spoken of the importance of protecting the environment, and according to Vatican officials, is committed to saving energy at the Vatican. The Vatican has said its aim is to use renewable energy sources for 20 per cent of its energy needs by 2020, the target date set by the European Union for its members.