I used 3.5 mil clear plastic from the paint section at Home Depot. It definitely works. It won't supress weeds and needs to be removed when planting unlike black plastic, but I think from reading a couple studies it works better at warming. Anyway, they didn't have the black.

I thought the black plastic is better to absorb the heat. I can be wrong.

They work differently - the black plastic absorbs and radiates the heat but the clear plastic allows the sun's rays to penetrate and traps them.

http://umaine.edu/publications/2752e/

I can never find black plastic locally when I need it, so I order it fromPinetree Garden Seeds. For me it's cost effective, but I don't have a very large garden. I leave it on all season and plant straight into it. I've never been able to reuse it because it's thin and gets torn and beat up. I feel environmentally bad about that, but my soil needs help warming up in spring, and after that it helps keep down the weeds. Some rain water gets in, but it blocks most of it. But we don't get rain in the summer, so I use soaker hoses under the plastic to water. HTH.

The black plastic may come in different thicknesses. The thicker will last several seasons and washing it isn't necessary. Black isn't as warm as clear, but clear is too hot and will let weeds grow under it.

It-100 is an opaque brown that lets some heat through and doesn't let weeds grow. It is thin but can last for several years if carefully used. Fedco at least used to sell it.

Yeah the clear plastic works a little too well, I have large summer weeds growing under it!

You want the embossed plastic mulch, which stretches rather than tears.

Black Plastic Mulch