Editor's note: CNN International's Eye On series is visiting Poland. Read and watch reports from the country online and on TV until June 8.
(CNN) -- It was once that a cassock, a simple cross and a chalice was all you needed to equip the average church, but now the world of liturgical accessories is a big business.
Poland's SacroExpo is one of the largest trade fairs of its type in the world, hosting displays of everything from bells to church alarm systems and evangelical multimedia.
"We've even had electronic Bibles and electronic rosaries, confessional boxes with air-conditioning and heating and special priest vestments equipped for war zones," explains Andrzej Mochoń, President of Targi Kielce, the organizer of SacroExpo.
"The electronic Bibles have been especially popular with the elderly," he says, referring to the pocket PC-like devices which speak the Old and New Testaments.
The trade fair, now in its 13th year in the Polish city of Kielce, is officially called the International Exhibition of Church Construction, Church Fittings and Furnishings and Religious Art. It brings some 300 exhibitors from 15 countries and is now a fixture on the religious circuit. It attracts some 5,000 visitors -- most of these accredited clergy who are in the business of outfitting churches and priests with the accoutrements of the First Estate.
Globally the industry is worth an estimated $4 billion and runs from big ticket items like expensive musical instruments such as church organs to simple wooden rosary beads, which can sell for as little as a few dollars.
"Probably one of the most expensive everyday item for a church would be a chalice for taking communion," says Mochoń. "These can be works of art made of silver or gold and new ones are made in workshops in Germany, the Czech Republic or Italy."
Some of the strangest items on the exhibitors' stands are church vestments designed for missions to war zones such as Afghanistan. These include camouflaged cassocks.
"It's also made of special material to withstand very extreme temperatures," says Mochoń.
There are also highly colored vestments for African priests and plain black favored by Poland's local Catholic priests. Other items include electric candles, automatic church bells and even heated pews.
The company that sells the pews, Polarheat, says that when the temperature in Poland drops to minus 10 degrees celsius it can be as cold as minus 15 in many churches.
"At that temperature, even the communion wine freezes," says a company spokesman. "It can be pretty uncomfortable."
Renewable energy is also becoming increasingly popular to heat church properties, according to Mochoń, not least ancient cathedrals which, because of their cold stone, high Gothic arches and vast planes of stained glass windows, are some of the most notoriously cold places in many European cities.
Other exhibitors point to new directions for the Catholic Church.
A wine company that sells communion wine for Holy Mass reports that priests are favoring whites over reds because the colorless liquid does not make stains on white robes.
The showpiece at last year's event was the reconstructed 18 meter-long "popemobile" of Pope John Paul II.
As well as devotional articles, such as crucifixes and sacral art, the trade fair is also an acknowledgement that churches, especially historic cathedrals, can be expensive to run and need skilled craftsmen to maintain.
Among the services displaying at the expo are internal architects, landscape gardeners, experts in cemetery maintenance and craftsmen that specialize in the manufacture of bells. Other services include agents for religious tourism and pilgrimages.
Pilgrimages to sites of special devotion have been a big business since the Middle Ages, but the ability of people to travel easily and cheaply has seen Catholic pilgrimages grow into a multi-billion dollar industry.
Lourdes in France, believed to be the site of several miracles, regularly attracts more than 5 million pilgrims a year, only slightly below the number one Catholic destination, Rome.