Blobs or boxes? What will the architecture of tomorrow - already emerging in some places - look like? This is the kind of frothy question that blockbuster international exhibitions such as the Venice Biennale like to ask: a question traditionally beyond the range of architecture books.

Ten years ago, however, the rules changed with the publication of S,M,L,XL by the Dutch architect Rem Koolhaas and the Canadian graphic designer Bruce Mau. A restless, jump-cut, novelistic collage stretching to more than 1,300 pages of essays, manifestos and travel diaries, S,M,L,XL contained more than 2,000 illustrations while its contents were arranged according to scale - from the house to the city. A big, beautiful brick of a book, it sold like crazy. Architectural publishing has not been the same since.

Perhaps the most successful of the new breed of bigger, heavier books was 10x10. Published five years ago by Phaidon, it used its monumental size - 468 pages (each 1ft square) covered with 1,500 illustrations - to undertake a global survey of millennial architecture.

The book's formula was simple: 10 prominent critics each selected 10 emerging architects and gave their views on contemporary trends, suggesting a battlefield of architectural ideas. The cover, adorned with fashionably Dutch black-and-orange super-graphics, used lenticular plastic film to create an interference pattern that imparted an ambiguous, elusive, three-dimensional quality to its surface.

The New York-based, German designer Julia Hasting's clever packaging created an object of desire, and sales of the thumpingly heavy 10x10 - the world's first exhibition-in-a-book - outstripped expectations, reaching an audience that few architecture books manage to do. Five years on, 10x10_2 follows in the footsteps of its acclaimed predecessor and presents 100 new faces chosen by a different set of critics - five from Europe, two from the Americas and three from the Asia-Pacific region.

The formula is unchanged, but this time Hasting's multilayered, laser-cut, white card cover and translucent plastic dust jacket create an impression of an architectural circuit board model. Inside, close-lined pages and computer-font texts suggest that in the 21st century architecture has gone digital, as last year's Venice Biennale proclaimed. But has it?

Devotees of the blob - an architecture of sculptural shapes made easier by advanced software programmes of the type pioneered in the design of Frank Gehry's Guggenheim Museum in Bilbao - will not be disappointed in 10x10_2, which reprises architecture's hottest topic of debate.

However, the evidence presented by this book (even its very existence) is proof that the paperless studio and rapid prototyping in architecture are still a long way off. A few notable exceptions apart, it appears that these curvy, fluid futures - soft spaces that seem permanently on the verge of melting, as in a surrealist dream - cannot be built and are condemned to exist as wraiths in the virtual world for the time being, at least.

The influential champions of digital architecture and parametric design in 10x10_2 include Frédéric Migayrou, the chief curator of architecture and design at the Pompidou Centre in Paris, Zaha Hadid, the Pritzker prizewinner, and - to a lesser extent - Kurt Forster, the director of last year's Venice Biennale.

It is strange that this seductive new wave in architecture, which sprang up on both coasts of America as well as in London, Paris and Rotterdam, should have left Ireland - one of the world's greatest producers of software - untouched. Perhaps it is because the movement remains more dependent on a small network of high-powered educational centres than it does on what's inside the computer. Networks count if you want to be in 10x10_2.

Nevertheless, two Irish blobs are among the 250 projects featured in the book. Migayrou selected Dagmar Richter's design for Waterford North Quays, a fluid megastructure based on the "waviness of a lock of hair", and Hadid chose Kas Oosterhuis's rubberoid, slug-like design for the U2 tower in Dublin's docklands. As it happens, both were unsuccessful competition entries for sites that had little by way of existing built context - the urban condition most suited to autonomous blob architecture.

It's not just blob architecture that is hard to build, though. In New York, for example, where there is little tradition of publicly funded architecture, emerging architects such as the Irish-American-Japanese Morris Sato Studio construct alternative forms of architectural practice by designing furniture, interiors, exhibitions and public art works (which they have built in America and Japan in collaboration with Jody Pinto, the artist).

Michael Morris, who won a Fulbright scholarship to Ireland in the early 1990s to study lighthouses (and also helped draw up Group 91's winning competition entry for the Temple Bar Architectural Framework Plan) and Yoshiko Sato were selected by Toshiko Mori, their former teacher in New York and Harvard.

Since their ethereal design for the Shiro Kuramata retrospective exhibition in New York and Montréal in 1998, Morris and Sato are regarded by many as the exhibition king and queen of New York. They have designed shows for the Smithsonian Cooper-Hewitt National Design Museum and the American Folk Art Museum and are developing a corporate history exhibition for the headquarters of American Express at the World Financial Centre, overlooking ground zero.

The house and 32ft-high studio they designed for Ezra Winter, the muralist, in Falls Village, Connecticut, was named North American home of the year in 2001. "We design air," says Sato. "We are searching for an ephemeral quality." Morris agrees: "What's important is the space between the user and the shell," he says.

That is not what motivates the designers of boxes, the prismatic containers on which all Modernist architecture is based. Every bit as image-conscious and fashion-driven as the shape-making blobbists, they are obsessed with the brilliant appearance of the skin of their buildings.

In 10x10_2, a mind-boggling array of external surface materials is on display: waxed plywood, bitumen-impregnated cardboard, polyurethane-coated compressed wood, rust-covered steel, glass tattooed with barcodes or cherry-leaf patterns, conveyor-belt mesh curtains, and even black rubber, customised with gill-like slits over the windows that add to the scuba look.

There is a third architectural way between the boxes and the blobs, however, which was represented in the first 10x10 by Ireland's de Blacam and Meagher, among others, who showed that tectonic integrity remains the key to authentic architecture.

Deyan Sudjic, director of the 2002 Venice Biennale, says his selection for 10x10_2 is "in part a response to the feverish rush to virtuality and the obsessive interest in shape-making that seemed to be the message from the first volume." He sought out architects "interested in the material qualities of architecture, who are enamoured of the quieter qualities of building."

Responding to Ireland's new visibility on the international landscape of contemporary architecture, he selected four projects by each of three prominent Dublin architects: Tom de Paor, Grafton Architects and O'Donnell + Tuomey. All three are veterans of the Venice Biennale.

Boyd Cody Architects from Dublin, founded in 2000, has enjoyed a meteoric rise: it was selected for 10x10_2 alongside the established Aires Mateus e Associados from Lisbon (currently building a luxury hotel in Dublin's docklands) by Alberto Campo Baeza, the Madrid-based architect. There is an Iberian quality to Boyd Cody's work: Dermot Boyd worked for Campo Baeza in 1989 while still a student and Peter Cody spent three years in Portugal in the 1990s in the office of Álvaro Siza, one of Europe's greatest architects.

Not yet 40 years of age, Boyd and Cody will be presented next month with the Architectural Association of Ireland's premier award, the Downes Medal, for their first free-standing building, a small, two-bedroom mews house built last year on a tiny site in Alma Lane in the south Dublin suburb of Monkstown. They are the first of their generation to win the medal.

The AAI jury included Terence Riley (the Phillip Johnson chief curator of architecture and design at the Museum of Modern Art, New York) who was a critic for 10x10, as well as a pair of architects featured in 10x10_2: Rotterdam-based Kees Kaan of Claus en Kaan Architecten, selected by Sudjic, and Manuel Aires Mateus.

Overlapping networks characterise today's architectural scene. Among those featured in 10x10_2 who will visit Cork, the European Capital of Culture, next June for a symposium linked to the New Trends of Architecture in Europe and Asia-Pacific exhibition are: Atelier Bow-Wow from Japan, Atelier Feichang Jianzhu from China, Kerstin Thompson from Australia, Jürgen Mayer H from Germany, Ocean North from Finland and Sadar Vuga Arhitekti from Slovenia. They will be joined by architects from the first volume, Shigeru Ban and Kengo Kuma from Japan, and d'ECOi from France.

Campo Baeza quotes a Nazarene proverb in 10x10_2 that provides a lyrical recipe for construction: "To make a house," it directs, "you grab a handful of air and hold it together with a few walls." As with Morris Sato's Winter studio in Connecticut, that is just what Boyd Cody's tough, crisp little cube of brick and glass manages to do.

10x10_2, curated by Miquel Adrià, Alberto Campo Baeza, Kurt Forster, Zaha Hadid, Davina Jackson, Jong-Kyu Kim, Frédéric Migayrou, Toshiko Mori, Deyan Sudjic and Edwin Viray, is published by Phaidon Press on March 28, 2005, price €75/£45. www.phaidon.com