Fleece thickness

I got some fleece, and took a chance with some lettuce and carrots in the garden, close by so i can cover at night if needed. Is the fleece thick enough its seems thin but B&Q seem to think it is good enough or i have some terram that is super think that i could use.

If you double up the thickness of cheap fleece do you get double the protection?
Or enough to get through spring frosts?

I bought the 'thinner' variety Kris describes and found it was hit and miss with frosts. If it was a particularly cool night with harder frost, I lost everything under that fleece. I tried doubling and it helped but it was more trouble to do so. So I bit the bullet and bought a heavier weight fleece that is perfect and heavy frosts can come and go with no worry to me. Soon as I think frosts have passed, I fold them up carefully and store them indoors. I expect to get many years use out of the heavier one. The thinner ones are already falling apart and they weren't cheap.

Some of mine is from the pound shop. You can only give it a try.