Design Mode is one of the four modes in Foldit's original interface. Design mode can only be used on design puzzles. Some or all of the segments in a design puzzle are mutable. In design mode, clicking on a mutable segment displays a wheel menu which allows you to change the segment's amino acid.
The outer ring of the wheel menu has an orange background, and contains 11 hydrophobic amino acids. These amino acids are most likely to be found inside the protein, away from water. Hydrophobic amino acids on the outside of a protein are known as exposeds, and score poorly in Foldit.
The inner ring has a blue background, and contains nine hydrophilic amino acids. These amino acids are more likely to be found on the outside of a protein.
Some design puzzles also allow segments to be inserted or deleted. In design mode, right-clicking (or control-clicking) on an eligible segment brings up the insert/delete wheel menu, which allows you to insert or delete one or more segments.
Deleting segments may sometimes eliminate problems, such as a filter penalty for "non-ideal" loops. The drawback is that each segment contributes the the overall score for the protein, so deleting segments lowers the best possible score.
In the other direction, design puzzles may have a defined maximum number of segments. Inserting segments beyond this maximum may incur a filter penalty, which normally cancels out the score gains from the added segments.
Some design puzzles may also include a filter which imposes a smaller penalty for added segments. For example, Puzzle 1364 started with 65 segments. Each added segment up to a total of 100 segments incurred a small penalty to partially offset the added score.