A reaction mixture for producing a film-forming polycarbosilazane polymer comprises a first compound containing at least two unsaturated groups and a second compound containing at least two SiH.sub.2 hydrosilyl functional groups, wherein the reaction mixture is capable of forming the film-forming polycarbosilazane polymer utilizing hydrosilylation of the first compound by the second compound. Also disclosed are methods of forming a silicon and carbon containing film on a substrate comprising the steps of producing a film-forming polycarbosilazane polymer by a polymerization of a reaction mixture of a first compound containing at least two unsaturated groups and a second compound containing at least two hydrosilyl functional groups, forming a solution containing the film-forming polycarbosilazane polymer, and contacting the solution with the substrate via a spin-on coating, spray coating, dip coating, or slit coating technique to form the silicon and carbon containing film on the substrate.

A gas barrier film comprising a resin base material, an oxygen barrier coating provided on at least one surface of the resin base material, and a base layer and/or an inorganic oxide layer provided between the resin base material and the oxygen barrier coating, wherein the black area ratio of one surface measured by the following measuring method is 0.15% or less: <Measuring method> An arbitrary region of 1281 m square on one surface of a resin base material is photographed with an optical microscope to acquire a photographed image of 10241024 pixels, the photographed image is converted into a monochrome image of 256 gradations using an image analysis software, and the value obtained by subtracting 30 from the most frequent value of the luminance in the monochrome image is set as the threshold, the value less than the threshold is set to black, and the value not less than the threshold is set to white, thus binarizing the luminance, and the ratio of the total area of the black regions having a size of 100 m.sup.2 or more in the 1281 m square region is defined as the black area ratio.

A stress relaxation gas barrier film, including one or more cured film layers and one or more stress relaxation layers alternately stacked, the one or more cured film layers being a cured product of a polysilazane composition containing a polysilazane compound represented by the following formula (1):

##STR00001## the one or more stress relaxation layers being a cured product of a silicone resin composition containing a linear organopolysiloxane represented by the following formula (A-1), and each having a film thickness of 0.1 to 15.0 m:

##STR00002##

This can provide a gas barrier film with stress relaxation properties such that uniform application to a film or polysilazane resin is possible and workability does not deteriorate.