The 9.5mm film format was successfully introduced by the Pathé Company together with the Pathé Baby projector in 1922. Nine months later, in July 1923, the Pathé Baby camera was launched, which, furthermore, introduced a new type of film – a reversal film, which made shooting easier and, above all, reduced film processing costs. This film, also known as a “direct positive", had the advantage of bypassing the traditional step of making prints from a negative. In this case, a special chemical treatment transformed the negative image into a positive on the same film. This economical solution was an obvious choice for film manufacturers Pathé and Kodak, who each created their own reversal process for their respective formats 9.5mm and 16mm. In fact, the use of reversal film went on to define the practice of small-gauge cinema throughout its history.

Georges Zelger, a chemical engineer, began trials on the composition of a reversal emulsion and its processing method in December 1922, under the direction of Jacques Pathé, Charles Pathé's nephew who had been appointed to the commercial management of Pathé-Baby. At the same time, Continsouza Manufacturing (Établissements Continsouza), Pathé's camera manufacturer, had been working on the design of a simplified camera since January 1922. Unlike Kodak – which adopted a complex inversion method involving a second light exposure, followed by a second processing step – Pathé's film processing was designed to be as practical as possible, so that it could be carried out by relatively inexperienced amateurs. Their method transformed the negative into a positive through a series of chemical baths, a much easier process to carry out than a second light exposure. The final step, blackening the unexposed silver halide crystals, is completed in a sodium hydrosulfite immersion bath. This formula was patented. The engineers also designed a handy development kit, consisting of a small individual tank and ready-to-use product doses. The kit was made available to the public, enabling home processing. However, in practice, Pathé-Baby customers would often entrust film processing to professional laboratories. As soon as the camera was put on the market, the Joinville-le-Pont factory set up an amateur film processing unit, headed by Louis Didiée. However, given the highly convenient nature of the method, many Pathé-Baby retailers were able to offer this processing service in their shops.

In 1927, the film manufacturing factory in Vincennes became Kodak-Pathé. The new company continued to manufacture film specially created for Pathé-Baby. Reversal films followed the same developments as professional films. The Société française du Pathé-Baby released a panchromatic reversal film in 1932, and super-sensitive, fine-grain films the following year. During the 1930s, the number of rival film manufacturers multiplied. As a sign of Pathé-Baby's commercial success, there were no less than ten different French and European brands offering 9.5mm film. In color, Dufaycolor was issued on 9.5mm in 1936–37, albeit hesitantly. It wasn't until January 1951 that 9.5 mm Kodachrome was released, enabling the format to catch up with 16mm and 8 mm.

Kodak-Pathé remained the main supplier of raw 9.5mm film, long after Pathé had abandoned the format, until 1976, when 9.5mm Kodachrome was discontinued. After this date, amateurs could still purchase film, thanks to the dedication of a few entrepreneurs and enthusiasts. Ligonie, a 9.5 mm equipment manufacturer, packaged Ektachrome in 9.5mm reels. The legacy was then carried on by 9.5 cine clubs like SACOM 9.5 and SEF 9.5. Using industrial machines salvaged from factories, they perforated and slit 35mm film into 9.5mm, using reels of raw reversal film, such as Gevachrome or Fujichrome. The last production runs were carried out by the Cinédia laboratory in 2014. However, in June 2023, the format was revived when the French company Color Films Archives announced the launch of 9.5mm Kodak Ektachrome 100D film, again slit down from 35mm.