Most duct tapes are water-resistant but not entirely waterproof. Duct tapes feature a polyethylene backing that provides a degree of water resistance, making it effective for short-term applications where it might be exposed to small amounts of moisture. But duct tape's water-resistant properties do have limitations.

Prolonged exposure to water, especially in harsh conditions such as continuous heavy rain or submersion underwater, can quickly reduce the adhesives effectiveness. Over time, the adhesive may weaken, and the tape itself may break down, diminishing its ability to provide a reliable seal against water penetration.

Water-resistant VS Waterproof

Water-Resistant: Water-resistant tape can resist the penetration of water to a certain degree but won’t hold a water-tight seal for long. 

Waterproof: Waterproof tapes are designed to provide a water-tight seal and do not allow water to penetrate. 

For applications requiring a higher level of water resistance or waterproofing, you might consider a tape like Water Guard™ Permanent Waterproofing Tape. While it isn’t a duct tape, Water Guard™ is a permanent waterproof tape commonly used for sealing, securing, and waterproofing. Water Guard™ can also be applied underwater!