ShadeMart 18 ft x 21 ft Blue Sun Shade Sail UPF50 Rectangle - Heavy

Our review of the ShadeMart 18' x 21' Blue Sun Shade Sail finds it best for homeowners and RV owners who need broad, breathable UV protection for patios, carports or outdoor seating areas. The single biggest reason to buy is the heavy duty woven HDPE fabric and stainless steel corner D rings, which combine to deliver durable, tension-ready shade that blocks up to 95% of harmful UV while remaining water and air permeable. It is a practical, decorative large rectangle sail that lowers temperatures and stands up well in windy conditions when properly installed.

Key Features

• Material: The woven HDPE fabric provides a tough, tear-resistant surface that tolerates outdoor use and resists fading in hot weather.
• UV Protection: Blocks up to 95% of harmful UV rays to significantly reduce heat and protect vehicles, furniture and skin under the canopy.
• Breathability: Water and air permeable construction allows rain and wind to pass through, reducing flap and pooling during storms.
• Hardware Ready: Stainless steel D rings attached to heavy duty webbing make secure anchoring to poles, walls or trees straightforward.
• Custom Sizing: A range of custom size options is offered so buyers can choose dimensions that best fit patios, poolsides or carports.
• Styling: The rectangle shape and color choices act as a decorative canopy that integrates with existing outdoor design.

Who It's For

This shade sail is ideal for homeowners, RV owners and gardeners who want a large, durable sun screen that reduces temperature and provides reliable UV protection without becoming a solid rain barrier. It suits patios, pergolas, carports and poolside areas where airflow and reduced heat are priorities.

People who need a fully waterproof solution or require a precise off-the-shelf color match should look elsewhere; this style is explicitly not waterproof and customers report mixed feedback on exact color and measured size differences, so careful measurement and realistic expectations about shade color are important.

Pros & Cons

Pros

• Durable woven HDPE fabric and stainless steel D rings provide solid build quality and long service life.
• Excellent UV blocking performance lowers surface and ambient temperatures under the sail.
• Water permeable design prevents pooling and allows airflow, reducing stress in wind.
• Easy to install and looks attractive when tensioned, enhancing outdoor spaces.

Cons

• Not waterproof, so it will not keep areas dry in heavy rain.
• Color may vary from photos and manual measurements can differ from stated dimensions, so order carefully.

Specifications

Brand	ShadeMart
Shape	Rectangle
Size	18' x 21'
Material	Woven HDPE (High Density Polyethylene)
UV Protection	Up to 95% UV block (UPF50)
Hardware	Stainless steel corner D rings on heavy duty webbing
Water Resistance	Water and air permeable (not waterproof)

Our Verdict

The ShadeMart 18' x 21' Blue Sun Shade Sail is a good value for anyone seeking a large, durable, breathable sun canopy that cuts UV and heat while remaining decorative. It performs well when tensioned with proper hardware and is particularly suited to patios, carports and RV covers; choose carefully on color and measure twice before ordering to avoid sizing disappointments.

Frequently Asked Questions

Is this shade sail waterproof?
The fabric is water permeable and breathable, not waterproof, so it will not provide full rain protection.

Can it be installed on trees or poles?
Yes, the stainless steel D rings and heavy duty webbing allow attachment to poles, trees, walls or roofs with appropriate hardware.

Will it block UV and reduce heat?
Yes, the HDPE weave blocks up to 95% of harmful UV and can lower temperatures under the sail by noticeable degrees.