Medela nipple shields have two parts: a soft, flexible silicone membrane that is comfortable for sensitive skin and an outer shell with ventilation holes to let the skin breathe. They adjust to each other easily:

Fit the membrane tightly around the outer shell.
Place the assembled nipple shield inside the bra with the membrane opening centered over the nipple. The holes must face upwards.
Some of your breast milk may collect in the nipple shields when you use them. You should not give this milk to your baby. Throw it away when cleaning the protectors (see below).

How do nipple shields work?
Nipple shields fit inside the bra to prevent the fabric from rubbing against sensitive or sore nipples, allowing the skin to recover and promoting regeneration. It's a good idea to wear a nursing bra when using nipple shields, as they tend to be a little roomier than typical bras, making it easier to fit them in. However, you don't need to worry about Medela nipple shields showing through clothing, as their discreet shape ensures a natural look. You can use nipple shields continuously between breastfeeding sessions, but avoid using them in bed at night as it can worsen nipple pain.

Comfortable soft silicone bottom, comfortable for sensitive skin

Ventilation holes allow skin to breathe, promoting recovery

Flexible, to adapt to the shape of your breast

Can be used throughout the day, between breastfeeding sessions

They look natural under your clothes