A 3D car is grabbed and rotated by a user. (Credit: Iñigo Ezcurdia 2025)
In a nutshell
- Spanish researchers created FlexiVol, a 3D display with elastic materials that lets users reach inside and directly manipulate digital objects with their bare hands
- Users completed tasks nearly twice as fast using reach-through interaction compared to traditional 3D mouse controls, with lower mental workload
- The technology could transform fields like education, design, and museum exhibits by letting multiple people collaborate with 3D content without needing VR headsets
PAMPLONA, Spain — Forget headsets and gloves. Spanish scientists have created something far more intuitive: a display that lets you stick your hand right into a holographic 3D image and touch virtual objects floating in mid-air.
The revolutionary tech by researchers from Spain’s Public University of Navarra is called FlexiVol. It replaces the rigid components of traditional 3D displays with elastic materials that safely bend around your fingers when you reach through them. Unlike virtual reality which isolates you behind a headset, FlexiVol brings digital objects into your physical space.
“What we see in films and call holograms are typically volumetric displays,” says Dr. Elodie Bouzbib, the first author of the work, in a statement. “These are graphics that appear in mid-air and can be viewed from various angles without the need for wearing virtual reality glasses. They are called true-3D graphics.”
Participants initially approached the system with caution. According to the paper, some thought reaching through the diffuser “would hurt, but it did not,” while others worried “the diffuser displacement would bother them, but it did not.” Most described the interaction as unexpectedly soft, with some finding it “quite pleasant.”
Asier Marzo, the lead researcher, explains that direct interaction means “being able to insert our hands to grab and drag virtual objects.” He adds: “We are used to direct interaction with our phones, where we tap a button or drag a document directly with our finger on the screen – it is natural and intuitive for humans. This project enables us to use this natural interaction with 3D graphics to leverage our innate abilities of 3D vision and manipulation.”
Two people observing a 3D skull. One of them is touching the eye hole. (Credit: Iñigo Ezcurdia 2025)
How FlexiVol Works
The technology projects slices of 3D images onto elastic strips that oscillate rapidly up and down. Volumetric displays have a fast oscillating sheet called a diffuser, with images projected synchronously at high speed (2,880 images per second).
“The problem,” notes the research team, “is that the diffuser is usually rigid, and if it comes into contact with our hand while oscillating, it may break or cause injury.” To address this, the team replaced the rigid diffuser with an elastic one after testing different materials for their optical and mechanical properties. The challenge is that “elastic materials deform and require image correction,” adds Bouzbib.
Faster and More Intuitive
When comparing FlexiVol to traditional 3D mouse controls, the researchers found significant advantages:
- Selection tasks were completed in nearly half the time (1.0 seconds versus 1.9 seconds)
- Mental workload was substantially lower as measured by NASA’s standard cognitive assessment
- Nearly 90% of participants preferred the reach-through approach
“Commercial volumetric displays such as the Voxon VX1 use traditional mouse and keyboard techniques, or 3D mice as an input modality. Voxon displays also support a hand-tracking device (Leap Motion, Ultraleap Ltd.) enabling the use of the hands to manipulate virtual objects, but the real hands have to remain
outside of the display volume,” the paper notes.
FlexiVol changes this, and the effects were quite positive. One participant described feeling “more confident” when using their hands directly to interact with the 3D objects.
The technology isn’t perfect—the 3D mouse still offered better precision for fine movements. Users averaged 18mm positional error with the mouse versus 22mm with direct hand interaction. Physical fatigue was also higher when holding an arm extended into the display versus resting a wrist on a desk.
FlexiVol is a volumetric display with an elastic diffuser that allows users to reach inside and interact directly with true 3D graphics. The user input (hand) is aligned with the output (rendered objects), allowing to directly 1. grab virtual objects, 2. to translate and 3. rotate them.
Beyond Entertainment
This innovation enables new ways to interact with 3D graphics. “For example, grasping a cube between the index finger and thumb to move and rotate it, or simulating walking legs on a surface using the index and ring fingers,” the researchers illustrate.
“Displays such as screens and mobile devices are present in our lives for working, learning, or entertainment. Having three-dimensional graphics that can be directly manipulated has applications in education — for instance, visualizing and assembling the parts of an engine. Moreover, multiple users can interact collaboratively without the need for virtual reality headsets. These displays could be particularly useful in museums, for example, where visitors can simply approach and interact with the content,” explains the research team.
Bouzbib highlights that volumetric displays “are particularly interesting as they allow for the ‘come-and-interact’ paradigm, meaning that the users simply approach a device and start using it.”
The research will be presented at the CHI Conference on Human Factors in Computing Systems in Yokohama, Japan, April 26-May 1, 2025. This research is part of the InteVol project, led by UPNA and funded by the European Research Council (ERC), which funds the most prestigious research within the European Union.
By removing the barrier between humans and digital content, FlexiVol represents a fundamental shift in our relationship with technology. Instead of adapting our behaviors to computers through abstract interfaces, this technology brings digital objects into our physical world in a way that aligns with our natural human instincts to reach out and touch.
Paper Summary
Methodology
The team built volumetric displays using elastic materials instead of rigid components. They tested various materials including elastane fabrics, silicone, and elastic bands, evaluating their optical properties and flexibility. Their main test unit modified a commercial display with seven elastic strips. For testing, 18 participants performed selection, tracing, and docking tasks using both the reach-through system and a traditional 3D mouse.
Results
Users completed tasks significantly faster with the reach-through interaction compared to the 3D mouse (selection tasks: 1.0 vs. 1.9 seconds; docking tasks: 3.9 vs. 4.6 seconds). Mental workload scores were lower for the direct interaction method. The tradeoff was accuracy—positional error averaged 22mm with direct interaction versus 18mm with the 3D mouse. In feedback, 89% of participants preferred the reach-through method, describing it as more intuitive.
Limitations
The current prototype offers a relatively small display volume and modest resolution. Hand tracking accuracy presents challenges, especially for quick movements. Physical fatigue can occur when holding arms extended for long periods. The precision limitations of finger interaction compared to mouse controls remain a challenge, similar to early touchscreen interfaces versus mouse pointers.
Publication Information
The paper “FlexiVol: a Volumetric Display with an Elastic Diffuser to Enable Reach-Through Interaction” was authored by researchers at Universidad Pública de Navarra in Spain and will be presented at the CHI Conference on Human Factors in Computing Systems in April 2025. The research received funding from the EU Horizon 2020 program and the European Research Consortium.
