Koi Pond Liners

Quick Answer EPDM rubber is the best koi pond liner material — fish-safe, UV-resistant, and flexible enough to last 20-30 years. Look for 45 mil thickness specifically for koi ponds; thinner 20 mil liners (common in budget LDPE/HDPE options) are more vulnerable to punctures from koi’s sharp fins, rocks, and general pond activity over time.