shade cloth

Hoping someone can help sort out my thinking! I have a polytunnel...actually almost 2 of them, but one is just a tunnel and can't be ventilated very well and gets too hot in summer. I was going to use some sort of shade cloth to cool things a bit...but most shade cloth is dark and I was concerned if the dark shade cloth was actually draped over the plastic...the dark colour would absorb more heat, transfer heat to the plastic..hence the tunnel, actually making it even hotter.....

I have used bed sheets purchased at a junk store with acceptable results.  I suspect an air space between the shade fabric and plastic would help.

All the shade cloth I have purchased is an open-weave type thing that allows good ventilation. I don't know if I would put it on top of plastic, I agree with John that some space might help. Even raising the sides of the tunnel, maybe?

There are people in my area who "paint" on agricultural lime like a white wash to help shade their green houses. It washes off in the winter rain.

There are other people who run strings over the outside and grow climbing edibles (pole beans and tomatoes are the two I'm aware of, but I think in warmer climates, sweet potato vines may have been used this way). Living plants do a great job to shade and cool. You may be too hot for this approach depending on your weather.

Judy J Johnston wrote:...I was going to use some sort of shade cloth to cool things a bit...

If I may kindly suggest looking into 'No-See-Um' Netting (aka Mosquito Netting) expressly from this Co. Skeeta  ..in-particular, This stuff: No-See-Um  (and, No - I am Not a 'shill' or Sales Rep, etc - Just a Happy Customer

Benefit (over "Shade Cloth") is:

- Much Cheaper (per sq. yd.) and it can be Sewn into Very Large 'screens', by Skeeta, there.. ie: Last We ordered one for Our purposes, it was a 20' x 32' multi-panel 'screen' - $350.00! - that's Peanuts! (compared to That Much 'shade cloth')

- Super Tough material - withstands Winds, Rains, you name it - If it's Tough Enough for the Military to make 'Duty suits / Tents' out of - it's Tough Enough for the Garden.

- Easy to 'self-seam' (fold-over edges, use 'Carpet Tape' to secure, and/or 'iron-on fabric-patches tape' (just on LOW iron-settings.. and then Zip-tie / 'Tie-off' (paracord segments) to Secure to pipes.

- Also makes GREAT 'Coarse Filtration' material over your Rain-Catchment paradigms / Barrels, etc - Helps keep out Leaves / Dirt / Bird-Scootie, etc, etc.. And just 'hose off' / hang-dry to Clean.

The White No-See-Um will yield Approx. a '30 % Tint' (block about 30%), but thier 'Olive' or 'Grey' will block More - withOut 'adding heat'. You can Also simply 'double-up' the White,  for greater attenuation.

Fwiw, but We Love it (helps keep 'skeeters out of your Porch, too - Imagine that!

You're spot on about the dark cloth, it would just turn the plastic into a radiator. White or silver shade cloth is what you want, reflects the heat rather than absorbing it. And yeah definitely leave a gap between the cloth and the plastic if you can, even a few inches of airflow makes a big difference.