Rectangular Drop-In Liner

Custom-fabricated box-welded pond liner built to your exact dimensions. Professional-grade materials, precision-welded corners, and a perfect fit for rectangular ponds, tanks, and water features.

Get a Perfect Fit with a Custom Box-Welded Liner

Stop fighting with flat liner material. Our rectangular drop-in liners are custom-fabricated to your exact specifications. Each liner arrives ready to drop into your pond, tank, or water feature with factory-welded corners. No folding, no bunching, no guesswork.

Why Choose a Box-Welded Liner?

Unlike flat sheet liners that require folding and bunching at corners, box-welded liners are heat-welded into a true three-dimensional shape. This means cleaner installations, fewer wrinkles, and a more professional finished appearance.

Material Options

PP-45 (45mil Reinforced Polypropylene)

Our standard option for most pond installations. PP-45 features a woven polyester scrim core sandwiched between engineered coatings, creating a durable 45-mil liner. This material is stiffer and holds its shape well during installation. Fish-safe and backed by a 20-year exposed UV warranty. Best suited for ponds where all interior dimensions are 19 inches or greater.

• Thickness: 45 mil
• Puncture Resistance: 120 lbf min.
• 20-Year Exposed UV Warranty
• Low Temperature Rating: -50°F

XR-3 PW (30mil Reinforced Premium)

Our premium option featuring an EIA (Ethylene Interpolymer Alloy) coating with woven nylon reinforcement. XR-3 PW is thinner and more flexible than PP-45, making it easier to handle and conform to your excavation. Despite being 30 mil, the advanced construction delivers more than double the puncture resistance of PP-45. Required for smaller installations where any dimension is less than 19 inches. Suitable for potable water applications, aquaponics, and hydroponics.

• Thickness: 30 mil
• Puncture Resistance: 275 lbf min.
• 20-Year Warranty (when covered by soil or water)
• Low Temperature Rating: -30°F

Which Material Should I Choose?

For most backyard koi ponds with all interior dimensions of 19 inches or greater, PP-45 offers excellent durability at a lower price point. If your pond has any dimension less than 19 inches, XR-3 PW is required due to fabrication constraints. XR-3 PW is also the better choice if you prefer a more flexible liner that's easier to position during installation, or if puncture resistance is a priority.

Optional Add-Ons

8oz Geotextile Underlayment – A protective fabric layer installed beneath your liner. Helps prevent punctures from rocks, roots, and rough surfaces. Sold by the square foot to match your liner dimensions.

Continuous Flange Welding (Corner Fill) – Standard box-welded liners have small gaps at the flange corners, like the unsealed flaps of an open box. This upgrade welds those gaps closed, creating an unbroken flange around the entire perimeter. Useful when water needs to flow over the flange edge, such as with bog filters, spillways, or formal edge treatments. This is a fabrication detail, not structural reinforcement. The liner remains flexible regardless of this option.

How It Works

Use the configurator above to enter your pond's interior dimensions (length, width, and depth) along with your desired flange size. The flange is the flat lip that extends outward from the top edge of the liner. It gets sandwiched between your pond wall and the surrounding edge treatment (stone, decking, gravel border, etc.) to anchor the liner in place. We calculate the exact material needed and show you the price instantly. Your liner is fabricated to order and typically ships within 5–6 business days.

Before You Order

Measure twice, order once. These liners are custom-fabricated to your exact specifications, which means they are non-returnable. We can't restock or resell a liner cut to your dimensions. Take the time to measure your pond carefully. If you're not sure, contact us before placing the order and we'll help confirm the right dimensions.

Flexible, not rigid. This is a drop-in liner, not a free-standing structure. It requires a properly excavated hole or a supportive frame to maintain its shape. The corner fill upgrade does not change this. It is a fabrication detail, not structural reinforcement.

Minimum pond size. Most custom box-welded liners are fabricated for ponds of approximately 200 gallons or larger. Smaller projects may be outside our standard fabrication range. If the configurator shows "Contact Us to Order" for your dimensions, please reach out and we'll help determine the best path forward.