I did speak to the chap heading up the contractors who provide the sheets - just for you, DO, so don't get arsey with me.
The sheets are made of a flexible woven black plastic, like a lightweight but still fairly dense mesh. You can hold them up to the light and see through them, so they admit air, light and rain. They are, however, only good as frost protectors up to -4 degrees, beyond that, you're unlikely to get the protection you need, although he did say it would depend on how long the Clerk had grown the grass. As I've said before, the BHA recommends not less than six inches for NH and not less than a four-inch crop for the Flat, but some courses' growth is better than others. If the course hasn't been well cared for (and Plumpton has) then you may well end up with a very patchy surface in serious frost, as some parts would repel the stuff with the mesh and a good spread of grass, while others, cut or grown less well, wouldn't. (I would say it's like the difference between Richard Aldous now at Brighton, with good fields of runners in spite of the course's tricks, and the going produced by ex-Clerk Geoff Stickells, where the cut was often too short, the grass too thin, and the result was micro-fields.) The frost sits on the top of the sheet, as it sits on the top of anything, but doesn't work its way through, thus ensuring that it gets rolled up and off when the sheets are dragged off the ground. I tested the difference between the outside rails going and the parts where the sheets had been, and the sheeted portion was soft and spongey underfoot, giving a strong imprint and, like last meeting, a 'scalped' divot rather than an entirely pulled-up one. The feel under the good thick and long cut of grass on the unsheeted area was significantly firmer.
The sheets were hired by Cheltenham yesterday and worked by the same team which was hired for Plumpton. There were approximately 24 contracted staff working: sheet rollers of 3 per several sheets, a chap with a (hired) Loadall to pick them up with what look like pincers, and place the rolled sheets onto a Merlot with two front prongs. The Merlot then transported a number of these to a huge low-loader lorry with pivoting cab. The bigger Merlot (used at Chelt) will pick up to 4 tons in a shot, but today's was a wuss, only able to hoist up to 1.5 tons.
The sheets are also used for football pitches - up to 22 sheets will cover a pitch. Hot air blowers are used around the pitch under special tents which have to be erected. The blowers aren't used out in the open and the cost would be phenomenal around a course, especially one of Chelt's or Sandown's size. It would also be impossible due to the need to station several blowers all around the course, under tents (to stop wasting the hot air to the atmosphere) and using generators. Today, the supervisor said, was "a piece of piss" at Plumpton, as only around 130 sheets were laid - Cheltenham took around 360. The cost to Plumpton, he believed, was in the £30,000 mark.
There's no point in buying the sheets just in case you get one meeting likely to be lost to frost, though - they're very expensive to buy, you have to store them somewhere, and then you need the equipment like the Loadall and/or Merlot (the latter coming in at around £40,000+ I think) to pick the roll-ups. You would also need to bring in the groundstaff extra early for extra pay (they generally only start just before racing, attending the jumps) to do the work. And, judging by the provenance of many of them, I doubt they'd be up to the stooping required - all the attendants provided were husky young chaps!
Last stat: around 4 hours to lay out, 3 hours to pick up. The pick-up started just after 9.00 a.m.'s inspection today and was done by noon. The last roll-ups were collected just before first race.
I hope that helps.
