When worn during Rain, it protects against Wetness gain by 70%. Additionally, it insulates the player against Lightning strikes and the electric shocks of Jellyfish. It is also a tier 1 warm clothing, increasing the time a character can be without a fire during the Winter before Freezing. It has an insulation factor of 60, the same as the Rabbit Earmuffs.
Hamlet
The Snakeskin Jacket is also included in the Hamlet DLC, however, it has a very different appearance as Snakeskin is obtained from Vipers. It is especially useful by offering protection against Lightning strikes produced by Thunderbirds.
Trivia
Based on character examination quotes, the Snakeskin Jacket seems to have the same consistency of a leather jacket, explaining its mild insulation and high wetness protection.
The jacket appears to be sleeveless, as the characters appear to have their arms in the back, and the item itself has no sleeves.