A steel and tape tower, built then destroyed, is the spectacular openingshow of the Belfast Festival at Queen's. Karen Fricker reports

Since it was founded, in 1996, Improbable Theatre has lived up to its name by creating productions that don't much adhere to standard definitions of theatre - and often shouldn't work at all. A play about a poltergeist, featuring dolls made of Sellotape and newspaper (70 Hill Lane, seen at Dublin Theatre Festival in 1998); improvised story theatre based on a different audience member's life each night (Lifegame); a play about the inner life of the comatose (Coma); another about the company's interpersonal difficulties (Spirit). Not exactly traditional nights out.

But it is with Sticky, which opens the Belfast Festival at Queen's on Friday, that Improbable has pushed the notion of staging the unstageable to its limit. A collaboration with the London-based pyrotechnicians The World Famous, Sticky is a massive outdoor spectacle featuring a 100-foot tower, built before the audience's eyes from steel and sticky tape before collapsing in the space of the 45-minute performance; a DJ soundtrack of club and classical music; a bang-up fireworks display; and only one traditionally identifiable performer, an aerialist dressed as an insect who dangles high above the crowd from a crane.

"What I like about Sticky," says Phelim McDermott, one of Improbable's founders, "is that it is a celebration of a totally ridiculous idea. How can you make a building out of Sellotape? It's an impossible idea." And an intoxicatingly impractical one. Improbable charges £30,000, or almost €45,000, for each performance, although the total cost is more than twice that, according to Nick Sweeting, the company's producer (and another of its four founders, with McDermott, Julian Crouch and Lee Simpson).

And for all that expense there is no box-office income. Each of the 22 times it has been performed - in places from Stockton-on-Tees to Zurich to Sydney - it has been free to the public, the cost absorbed by the civic agency or festival that presented it.

As with most of Improbable's productions, Sticky is hard to describe. "I dream," sighs Simpson, "that one day we might create a show that is explainable in a sound bite." First there's its scale: 16 people, mostly local volunteers, perform the show, meaning they unravel tape and move large props, assisted by a dozen technicians; more than 6,000 people are expected to watch the Belfast performance, in the lower Botanic Gardens. That it is performed in a different setting each time also changes the way the show looks and the meanings it creates: the performance I saw last month, in the shadow of the London Eye, will doubtless feel very different to the one in sylvan south Belfast. The company has also layered possible interpretations into the show, to appeal across age ranges: what, to this adult at least, felt like a parable of creation, destruction and rebirth will probably come across to children as a really cool fireworks show.

Although this is Improbable's biggest show it is connected formally to 70 Hill Lane, its earliest production, in its use of tape as its central scenic element. "If the starting point of 70 Hill Lane was a roll of Sellotape and a newspaper," says Simpson, "then this one is Sellotape and a sparkler. The question is, can you take those things and make them magical? Can you transform the everyday into something that is uplifting spiritually?"

Although the company doesn't like titles, and works by mingling the roles of director, writer and actor, it is Crouch who is the principal design mind behind the team, and he has clearly spent a long time thinking about the creative and expressive potential of what most of us think of as ordinary stuff. Like tape. "I realised after many years of doing outdoor theatre that tape has enormous outdoor potential. Rain is always bad in outdoor shows, and the worst is wind - a sheet becomes a sail. But tape is like a net: it doesn't catch wind, the rain doesn't really affect it and it lights beautifully." Indeed, part of the unique experience of watching Sticky is being bewitched by the gorgeous, shimmering colours of its set, then realising that all you're looking at is light on cellophane.

All four core members say that, particularly now it has been running for a while, Sticky relies for its success on the skills of its technical crew. "They are the continuity, and they are vital, absolutely vital," says Crouch. "For me it's a bit utopian in a way. I think, of all the shows we have done, I am most proud of this one, because it's not just about the show. The most important thing is the team and how they work."

As a result, not every core member is required to participate in each Sticky performance; in London it was McDermott who had the luxury of just looking on - part of his attempts to take a creative sabbatical after several hectic years. In addition to almost non-stop creation and touring of Improbable productions, he and Crouch were also co-creators, for the London-based production company Cultural Industry, of Shockheaded Peter, a junk opera based on the macabre Struwwelpeter children's stories with a score written and performed by the Tiger Lilies. The show was an unprecedented hit that toured the US and the UK, including a run at the 1998 Belfast Festival at Queen's. Its success left McDermott and Crouch a little bewildered - a feeling they fed into Improbable's most recent show, The Hanging Man.

"It's about a guy who gets stuck between life and death," says McDermott. "He is an architect who was forced to take over a project when his mentor died and created an amazing building without thinking about it. Then he is asked to make another one, and he can't, so he tries to hang himself. It's like second-album syndrome. Having created Shockheaded Peter, people are saying to us, make another one. To move on from a big success you have to tune in to where you are, and that is where The Hanging Man came from." Having opened in Britain earlier this year, The Hanging Man is now touring the US.

Sticky has been part of Improbable's repertoire since 1998, but the company nearly struck it from its playlist after September 11th. "Our first reaction was, we can never do this again, a show about a tower falling down," says Sweeting. "But on reflection we realised that the tower can be a symbol for different things, and if you get anything from the storyline it's hope." Now that some years have passed, the company is working towards bringing Sticky to America - to Manhattan, even, if it can find a suitable site.

Meanwhile the Improbable minds are working together and separately on new and ongoing projects: their first co-production with the National Theatre in London, Theatre Of Blood, a stage adaptation of a 1970s schlock-horror film, goes forward next year; McDermott is developing a programme to use theatrical techniques and settings to resolve real-life conflicts; Crouch's freelance design career burgeons (he was designer and associate director of the smash hit Jerry Springer - The Opera); and Simpson happily continues his "day job" as a member of the Comedy Store Players.

"We still believe," reads Improbable's manifesto, "that one day a big red-faced man brandishing a stick will appear at the back of the theatre and shout 'Oi you bloody kids! Get out of it! Go on, clear off!' and we will be found out and have to run away." One hopes not. Theatre is much nurtured by its encounters with the improbable.

Sticky is at the lower Botanic Gardens, Belfast, on Friday at 6.30 p.m. (free)

Belfast Festival at Queen's runs until November 9th; you can get more details by calling 048-90272600 or by visiting www.belfastfestival.com. The Belfast box office is at 048-90272626; you can also book by calling 01-8721122