A joint investigation was launched Saturday into claims that a film-like material was found in the lining of winter school uniforms at a primary school in Chifeng, North China's Inner Mongolia autonomous region, according to the local authority.

In recent days, netizens in Harchqin Banner of Chifeng raised concerns online, saying they had discovered a plastic-like film in the winter uniforms of Jinshan No 3 Primary School and worried the material would cause poor breathability when worn by students.

An official with the Harqin Banner education bureau said Friday that staff members were conducting on-site inspections at the school alongside market supervision authorities.

The official noted that the uniforms in question are winter styles, adding that the fabric used had passed quality inspections.

The film-like layer, the official said, is likely a thermal insulation component, though further verification is underway.

Authorities said they will release updates on the probe's progress to the public in a timely manner.