Planting fleeces are used either for new seeds and seedlings, or they protect older plants from frost. Depending on the thickness of the fiber, they allow more or less light and water to pass through.
The thin, inexpensive variety is usually available in stores. Here you can see your own hand behind the fleece and it is very permeable to air. This fleece is good to use for the transition (March and April), when the weather still brings frost and sub-zero temperatures at night. Thin fleece can be used, for example, to protect the buds of hydrangeas from frost. During the day, the sun often shines warmly and the buds sprout. At night, temperatures cool quickly. An air-permeable layer protects the sensitive plants. During the day the fleece can be removed. If it is ever forgotten, no big deal, because it is so airy and light that no heat buildup will occur.
If it is thicker, similar to a linen fabric (a little less tight, of course), it is the thick fleece, which is often used for vegetable beds or to protect seeds. Here, as a sample, you can no longer see your hand well. However, for sprouted seedlings, the thicker fleece must have some distance from the seedling, otherwise the small plant will be crushed. You can achieve this by placing sticks or stones as spacers at the edges of the bed. In addition, from March onwards, you should always aerate during the day when temperatures are warm.
If it gets warmer from April, the thicker fleece in the vegetable garden can also be replaced by a thin, airy fleece.