Your bobbin thread should not show through the top layer of stitching. It will only be seen on the back of the item. The reason you want to use a lightweight thread is to avoid too much bulk on the back of the item.

Is bobbin thread visible?

You should never see the bobbin thread in the finished embroidery design. Ideally, some of your top thread should be pulled through onto the back side of your stitching. ... Very little bobbin thread should even be seen on the back of your embroidery!

Why can I see my bobbin thread?

- If the upper tension is too tight the bobbin thread with be showing on the top side of the material. Press the minus key on the screen to loosen the tension. - If the upper tension is too loose most of the upper thread will be showing on the bottom the material.