New research published in the journal i-Perception suggests that the way striped clothing affects body shape perception depends heavily on the specific spacing and direction of the lines. While people often believe that vertical stripes always create a taller and thinner look, this study provides evidence that horizontal pencil stripes can actually produce the most slimming effect. The findings offer practical insights into how simple geometric patterns alter our visual judgment of the human figure.
Scientists Tzu-Yu Chen, a PhD candidate at the Graduate School of Design at National Yunlin University of Science and Technology, and Li-Hsun Peng, a retired associate professor at the same university, conducted the study. They wanted to explore conflicting theories about visual perception and clothing patterns. A scientific concept known as the Helmholtz illusion suggests that horizontal lines can make a space, or a person, appear taller and narrower than vertical lines do.
Previous studies testing this illusion on human bodies have yielded highly inconsistent results. Peng noted that the goal was to expand upon basic theories of design. “In the field of design psychology, I wanted to move beyond the traditional binary of ‘horizontal vs. vertical stripes,'” Peng explained.
“Most existing studies focus solely on orientation, but our research demonstrates that the interaction between stripe type and stripe orientation significantly influences visual body perception,” Peng said. “Interestingly, our study also revealed that women tend to be more sensitive to these striped patterns than men when evaluating body image.”
Most people view full bodies in the real world and rarely compare horizontal and vertical patterns side by side. Clothing styles also impact a person’s body image, which is the subjective mental picture of one’s own physical appearance. People often buy striped clothing specifically to enhance this personal body image, making the optical illusion a highly practical topic for fashion design.
To address past inconsistencies, the scientists designed an experiment using images of a real human model. They categorized their patterns into two distinct types. The first category was equidistant stripes, where the dark lines and the light spaces between them are the exact same width.
The second category was pencil stripes. In these patterns, the light background spaces are significantly wider than the dark lines. The researchers recruited 241 undergraduate students from a university in Taiwan to participate in a visual survey.
They photographed a female volunteer model wearing a slim-fitting, short-sleeved dress. The model had a Body Mass Index of 20.8, representing an average to slightly above-average body type for Taiwanese women. The survey featured white dresses with black stripes in five specific measurements.
Three of these styles featured equidistant stripes, measuring one centimeter, two centimeters, or five centimeters in both line and gap width. The other two styles featured pencil stripes, using one-centimeter black lines separated by either two-centimeter or five-centimeter white gaps. The students viewed these images on computer screens and answered questions about the model’s appearance.
The survey was divided into three distinct experiments to isolate different visual effects. In the first experiment, the students looked exclusively at dresses with horizontal stripes. The results indicate that the horizontal pencil stripe with a two-centimeter white gap provided the most slimming effect, earning support from over half of the participants.
However, the horizontal dress with five-centimeter white gaps received the least support for a slimming effect. This suggests that horizontal pencil stripes only make a person appear thinner if the spacing is kept relatively narrow. The second experiment repeated this process using only vertical stripes, yielding highly inconsistent visual feedback among the students.
In the third experiment, the scientists asked the students to compare horizontal and vertical stripes directly against one another. To mimic real-world observation, they showed horizontal and vertical versions of the same dress on alternating screens. This forced the students to rely on short-term memory to make their evaluations.
“While a horizontal ‘pencil stripe’ pattern (1×2 h) can create a slimming effect, certain vertical configurations can achieve similar or even superior results depending on the perspective,” Peng said. “For example, in a standard 1×1 striped dress, our findings suggest that vertical stripes are perceived as more slimming than horizontal stripes when viewed from the back.” This highlights how a simple change in the viewing angle alters human perception.
While these findings are detailed, the study does have a few limitations to consider. The experiment only used one female model with a specific body type. This means the visual effects might differ on people with different body shapes, heights, or sizes.
“It is important to remember that the ‘1×2 pencil stripe’ may not be the optimal slimming choice for every body type, particularly for larger frames,” Peng noted. “Due to our focus on comparing five stripe types and two orientations, the primary experiment used a specific model prototype.” The students in the study were also all from the same demographic group, which might limit how these perceptions apply across different age brackets.
“For those with a fuller figure looking to utilize these illusions, our data suggests that 1×1 equidistant vertical stripes might be a more effective and reliable option than certain horizontal patterns,” Peng added. Future research could examine how these spacing patterns interact with looser clothing or different fabric types. Scientists might also test these optical illusions using a wider variety of colors.
The researchers also found unexpected potential for specific designs in maternity wear. “One of the most surprising findings was the potential of the 2×2 horizontal stripe as a functional choice for maternity wear,” Peng explained. “It manages to flatter the pregnant silhouette while remaining visually striking—blending aesthetic appeal with a degree of ‘visual safety’ (visibility).”
“On a personal note, during the course of this experiment, I happened to be pregnant myself and frequently wore these 2×2 horizontal striped dresses,” Peng shared. “Furthermore, when testing this specific pattern across eight different body types (ranging in height and weight), we observed a powerful hysteresis phenomenon.” A hysteresis phenomenon occurs when a system’s current state is highly dependent on its history, meaning the visual perception tends to remain stable even as the underlying body shape changes.
“The results were statistically non-significant across all eight body types for the 2×2 pattern,” Peng noted. “While we did not publish the non-significant data, this ‘neutrality’ is fascinating as it suggests a versatile design option that remains visually consistent regardless of the wearer’s size.” This suggests that some patterns neutralize body shape differences almost entirely.
The study, “The influence of striped clothing on visual body perception: A study on pattern spacing design,” was authored by Tzu-Yu Chen and Li-Hsun Peng.