If the negative is polyester base, those sleeves are probably ok as long as they are of archival material, and free of powders, etc. But if the film is triacetate base (still very common, more so in roll formats), those sleeves are not recommended for long term storage. Triacetate films should be stored in "open" containers such as archival paper envelopes (not gastight) loosely placed in open storage area, adjusted to low humidity, if you want the film to keep for many decades.

Early triacetate films from 1950s stored in enclosed containers began to degrade in 1980s. But those stored in open containers are ok.