The best shade cloth for greenhouses

70% is the density most greenhouse guidance converges on, and for a reason worth understanding: the light inside a greenhouse has already lost some intensity to the glazing, but the heat has been concentrated by it. You are not shading a bed; you are trying to break a greenhouse effect.

Knitted HDPE, up to 70% UV block, breathable. The breathability is the part that matters most in a greenhouse context. A solid or waterproof cover over glass creates a sealed air gap that traps heat between the cover and the glazing — a knitted mesh lets that layer vent, which is the mechanism by which external shading actually cools a house.

It is also the Coolaroo line published in every useful roll size — 6 x 15 ft, 6 x 50 ft, 6 x 100 ft and 12 x 50 ft. A 12 ft width will go over the ridge of most domestic greenhouses in one piece, which means no seam along the top and nothing for wind to lift.

Colours run to seven options, which sounds cosmetic and is not: on a greenhouse, a lighter colour reflects more of what it blocks rather than absorbing it and re-radiating downward. Black cloth blocks the same percentage and gets hotter doing it.

No warranty term is published on the screening line, unlike the 50% Garden Cover and 90% Sun Protection, both of which carry fifteen years. Coolaroo positions this line as privacy screening, which is likely why — but not published is not published.

50% is the density for a greenhouse in a climate where the season is short and the concern is a handful of extreme weeks rather than a whole summer of overheating. In those houses, 70% costs you growing days at both ends.

Knitted HDPE in a mono/mono construction, up to 50% UV block, breathable to air and water. Monofilament in both directions is the more dimensionally stable weave, and on a greenhouse — where the cloth is stretched over a curved or pitched roof and pulled at the edges — stability is worth more than on a flat bed.

Fifteen years of fabric warranty against cracks, splits and tears due to UV degradation. The longest published term on any shade fabric we track. On a greenhouse cloth, which sits in full unfiltered sun on the outside of the glass for months, that is coverage of the exact failure mode.

Sizes 6 x 15 ft, 6 x 100 ft and 12 x 50 ft. The 12 ft width goes over the ridge of a typical domestic house; the 100 ft roll is enough for a run of cold frames as well.

Be honest about your climate before choosing it. In a hot summer a 50% cloth over glass will not be enough, and you will be back buying the 70%.

90% is the density for propagation houses, for shading cuttings and seedlings under glass, and for glasshouses in genuinely hot climates where the summer problem is survival rather than comfort.

Knitted HDPE in a tape/mono construction, up to 90% UV block, with air flowing through the knit. The tape/mono weave is how it reaches that density without becoming a solid sheet — tape in one direction for coverage, monofilament in the other for stability and airflow. A 90% solid cover would trap a superheated layer against the glass; a 90% knit vents it.

It carries the same fifteen-year fabric warranty against cracks, splits and tears due to UV degradation as the 50% Garden Cover, which makes it the best-warranted dense shade fabric available for this job.

Sizes 6 x 15 ft, 6 x 50 ft, 6 x 100 ft and 12 x 50 ft.

The failure mode is using it as a default. 90% over a greenhouse growing tomatoes will produce plants and very little fruit. It is a specialist density for a specialist job, and it is the right answer only if propagation or survival is genuinely what the house is doing in summer.

Greenhouses come in shapes that rolls do not: lean-tos, polytunnels with curved hoops, Victorian houses with a finial in the way. Custom cutting from 6 to 24 ft wide by 1 to 300 ft long is the practical answer to all of those.

It is the only fabric here publishing a GSM figure: 180 GSM knitted polyethylene, 75% block rate, up to 95% UV stabilized. 75% sits neatly between the 70% and 90% options above, and the GSM tells you something the percentages do not — 180 GSM is a relatively light fabric for that density, which means it will follow a curved hoop structure rather than fighting it.

A 3-year limited warranty, against Coolaroo's fifteen. That is the real cost of the custom sizing and it should be weighed honestly: on a greenhouse cloth living in full sun, twelve years of difference in UV coverage is not a rounding error.

Cut edge, no edge taping. You are finishing the edges and adding your own grommets or webbing. On a greenhouse this is more work than on a flat bed, because the fixing points are usually at the eaves where the load is highest.

The 24 ft maximum width is the useful number — wide enough to go over a full-span house and down both sides in one piece, which is the arrangement that survives wind best.

Included because the greenhouse question usually comes with a cold frame question attached, and a cold frame is a different problem: it is small, it heats fast, and its job in spring is hardening off rather than growing.

30% UV block on the same knitted HDPE. Enough to stop a frame cooking on a bright March afternoon, not so much that seedlings going out into the garden get soft. That is a narrower job than it sounds and 50% is genuinely too much for it.

Published only in 6 x 15 ft, which for a cold frame or a run of frames is exactly the right quantity and for a greenhouse is not.

No warranty term is published at this density, unlike the 50% and 90% Coolaroo lines.

Do not put it on a greenhouse roof and expect anything. At 30% over glass in July you will not be able to tell it is there, and that is the correct expectation rather than a defect.