Burri demonstrated his interest in the raw materials of picture making from his first works created in a prisoner of war camp in Hereford, Texas. Inspired by their inherent aesthetic qualities, he continued to widen his material vocabulary in the timber and miller's yards of Citta di Castello. Burri's unique manipulation of materials from both the artist's studio and the industrial yard served the expression of his ideas as a non-figurative painter. His principal aesthetic lay in the belief that a work should be directed by its medium rather than by ideas or realistic depictions.

It was in Texas that Burri first used jute sacking, initially as a support and then as an element of collage composition, this led to his famous and arguably finest works, the 'Sacchi' or burlap series of the early fifties. Burri combines the use of traditional paint with a 'rich play' of natural jute colours, textures and weave. The chance stainings and variety of coarse repairs in worn sacks are utilized to full effect, rents and holes are expanded into quais-geometrical openings or loosely stitched. In bringing out the subtleties of texture, colour and light with refined observation, Burri sought to raise materials otherwise disregarded to the 'dignity of Art' so that they might 'speak to the observer in advance of their associations.'

The collage of jute sacking has been noted by critics as Calvesi, Restany and Sweeney to have its direct parallel with surgery, and it does not surprise one that Burri had previously practiced medicine. The carnality of Burri's surface - slashed, sewn and bleeding - is suggested by the fraying ends of clumsily stitched sacking that hang open to reveal vibrant patches of red. However, as James Johnson Sweeney indicates "the picture is living flesh.... another moment and these sewn line take the character of landscape contours".

Bianco of 1952, from G. David Thompson's celebrated collection of Twentieth Century Art, emerges from a key period in Burri's development and represents a culmination of the ideas that had evolved from his early works. Burri imposes a serene geometric order in sharp contrast to his provocative use of materials which has been described as 'architectural in character' and which affirms his traditional education and need for order in a 'time of chaos'. Harmonising brown and ochre tones are emphasised in the adhered materials while the flat patches of white, black and red show the effective use of what Burri called his 'abstract colours'. The clarity of composition, the refined proportions and perfect balance of line, colour and texture show Burri to have arrived at a profound understanding of form that sets these works among "examples of the most disciplined visual intelligence". (Gerald Nordland)

From this period, such masterworks as the Grande Sacco and Grande Bianco at the Galeria Nazionale in Rome were born and from which later pieces as the Martedi Grasso at the Carnegie Institute evolved. The use of collage had found its precedent in the Cubists who used it as a means of identification with the fragmented object. The Dadaists and Surrealists had also advocated the de-naturing of objects of use. What makes Burri's contribution to collage unique is his exploration of the materials used in collage combined with formal analysis which enabled collage to stand as an art form in its own right.