A garden cloche allows your seedlings to be protected from germination to almost being potted out thanks to their little house above.
Glass is the traditional option and they are excellent at insulating your plants for warmth while allowing in the most light to help stimulate growth. They can be propped open at the bottom to allow for air circulation during the day. They come in multiple sizes. They are typically only suited for protecting one plant. Fleece and breathable mesh are another great option that allow for better air circulation and moisture, so they are great for protecting winter salads and other bigger veg. These have bigger options available that can protect two or more plants.