For better muffin shape, what should you avoid using in muffin tins?

Using paper liners in muffin tins, while common, can affect the muffin's shape and texture. When muffins bake with paper liners, they may not expand properly or rise as well since the liners can create resistance against the batter. Muffins need to be able to cling to the sides of the tin to rise correctly, and the use of paper liners can sometimes interfere with this process, leading to a slightly flat or uneven shape.

In contrast, parchment paper is specifically designed for baking and can enhance the muffin's ability to rise without straining against the liner. Wax paper and plastic wrap are not suitable for muffin tins because they are not heat-resistant and can melt or release unwanted substances into the batter, thus compromising both safety and the texture of the final product. Therefore, avoiding paper liners can lead to better muffin shape and quality during baking.