EnduraCap: Material Redesign

EnduraCap was created to address a common problem for continuous glucose monitor (CGM) users: overnight “compression lows.” When a user rolls onto their sensor during sleep, direct body weight compresses the device against the skin, constricting interstitial fluid flow and triggering false low glucose alarms. These inaccurate alerts do more than just disrupt sleep. They cause unnecessary stress and anxiety, and over time lead to alarm fatigue. In some cases, users may even treat a low that isn’t actually happening, creating genuine medical danger.

From the start, EnduraCap prioritized materials and production methods optimized for low-cost mass manufacturing. Engineering a functional device is essential, but ensuring that an effective defense against compression lows remains accessible and affordable to every patient who needs it is just as vital.

Figure 1: An original prototype of the EnduraCap made with low quality PLA and scrap memory foam. Additionally, a previously designed cover can be seen around the edges of the cap, though this is not within the scope of this project's redesign as the focus will only be on the cap portion.

To turn that concept into a working product, early development relied on fast, low-cost prototypes built from memory foam scraps and 3D-printed PLA. The combination was cheap and structurally tough, but real-world testing exposed flaws almost immediately. Under actual sleep loads, the memory foam completely collapsed. It compressed down until it bottomed out into a rock-hard layer, bulging out through the shell’s relief gaps. Instead of shielding the sensor, it jammed it straight against the rigid plastic frame, making the compression worse instead of better. Meanwhile, while the PLA outer shell offered good durability at a low cost, the raw 3D prints retained rough, prominent layer lines. Achieving a clean finish required extensive manual post-processing, making the manufacturing process far too labor-intensive and inconsistent for high-volume production.

Figure 2: The above image depicts a 3D rendering of one of the redesign concepts, with smoothed surfaces, rubber side grips, and a colorful foam layer underneath.

To resolve these limitations, the design transitioned to ABS for the outer shell. ABS offers superior impact strength, high heat resistance, and excellent structural stability, making it ideal for a durable, long-lasting protective shield. Additionally, for surface finishing, chemical smoothing via acetone vapor was tested; a process where acetone fumes gently melt the outermost layer of the plastic, fusing the ridges together to create a sleek, high-gloss surface that looks like an injection-molded product. Unfortunately, initial trials fell flat because the acetone solution used was not concentrated enough to generate the necessary vapor cloud. Despite that setback, the experiment yielded a crucial manufacturing takeaway. Setting up a sealed vapor chamber, safely managing chemical fumes, and waiting for the plastic to cure is highly efficient when processing hundreds of caps at once in factory batches. But at a smaller scale, simply using sandpaper to manually smooth just the top surface of the cap proved dramatically faster, required zero chemical setup, and delivered the exact skin-friendly smoothness needed.

This surface balance becomes even more critical when paired with the requirement for an adhesive-free design. Because medical tapes and adhesives frequently trigger skin irritation and allergic reactions, EnduraCap was engineered to be completely adhesive-less, securing itself solely through a precise, form-fitting friction fit around the sensor. However, relying strictly on a tight friction fit creates a new ergonomic challenge: the cap requires effective side grips so users can pull it on and off effortlessly. Interestingly, raw 3D-printed layer lines naturally produce a textured, high-friction surface along the outer walls.

This ultimately leads to a compelling hypothesis for future testing: does chemical smoothing cause more problems than it solves? Transitioning to targeted manual sanding on the stronger ABS material may prove far more effective. Sanding delivers a smooth, non-irritating top surface where the device contacts skin, clothing, and bedding, while remaining faster, safer, and completely chemical-free as well as eliminating any risk of weakening the structural integrity of the plastic. Furthermore, leaving the raw printed layer lines exposed along the vertical sides retains built-in, high-friction grips for effortless removal without the added cost of secondary rubber overmolds.

Figure 3: The triple foam layer deconstructured, engineered to maximize preotecction against compression while still staying structurally supportive.

As for the interior cushioning, testing evolved from simple scraps into a specialized three-layer stack engineered for customizability, structure, and protection. Initially, an outer EVA foam layer was used for its bright color options. However, to achieve a more refined, professional finish, future iterations will evaluate Sintra (expanded PVC) or separate, thin 3D-printed plastic color inserts, allowing effortless color swaps and personalization without sacrificing a polished look. Beneath that, a dense polyurethane foam core proved highly effective at absorbing compression forces while maintaining a snug fit, supported by a stabilizing layer of Poron directly above it to prevent the polyurethane from squeezing out through the shell's side gaps under sleep loads. Moving to a fully enclosed 3D-printed structure could eventually streamline this assembly, cutting down both material complexity and production costs. Finally, the overall depth of the ABS shell was extended to create a subtle clearance gap above the Dexcom sensor, preventing the rigid plastic frame from pressing directly onto the sensor body and relying instead on a thin, compliant foam pad to maintain a secure fit without transferring compressive force to the device beneath.

Beyond structural performance, the true value of EnduraCap lies in its potential for radical accessibility. Because the device relies on a compact form factor and ultra-thin layers of foam, the cost of materials stays under $1.00 per unit. By rejecting traditional medical markups, the product can be offered directly to patients at a very low retail price. Compared to out-of-pocket Continuous Glucose Monitor replacement costs that can exceed $100 and recurring monthly expenses for disposable adhesive patches, a one-time sub-$5 investment delivers an immediate return on investment, ensuring that safe, compression-free sleep is truly affordable for every one who needs it.

Just as crucial as the price tag is how easy this cap is to actually make. Right now, the design relies on a simple, single-part body that prints cleanly on a standard 3D printer without needing messy support structures, making local low-volume production effortless. If it scales up to high-volume manufacturing, the geometry is already simple enough to drop straight into a basic injection mold without needing a redesign, dropping the plastic cost to pennies a piece. Plus, because the internal foam stack is just a few thin, die-cut layers that sit neatly inside without adhesives, putting a unit together takes seconds. Whether printing 10 caps in a studio or molding 10,000 in a factory, the manufacturing process stays fast, cheap, and completely realistic, making it easy to keep the promise of affordable sensor protection for everyone.

Taylor Kaplan

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