Bionic Silicone Teat Engineering: Durometer, Flow and Latch
The bottle body wins the first order. The teat wins the next twelve. It is the part replaced every two to three months, the part in direct contact with a newborn's palate, and the part where most “bionic” claims quietly stop being true.
1. Why the teat carries the repeat business
Over a 0–24 month feeding cycle a single child goes through roughly 7–8 bottle bodies and 16–24 teats. The body is bought twice; the teat is bought eight or ten times. That asymmetry is why teat engineering deserves more attention than it usually gets in a product brief.
It is also the part where cheapness shows up first. A body that is slightly out of tolerance still holds milk. A teat whose durometer has drifted does not.
2. What suckling actually asks of the teat
Ultrasound studies of breastfeeding describe three mechanical events working together, not a single suction action:
- Tongue peristalsis. The tongue rolls in a wave from the teat tip toward the throat, compressing the teat as it goes. The tip has to extend axially — roughly 1.5–2 times its resting length in the softest designs — without collapsing.
- Mandibular movement. The jaw rises and falls against the areola zone, which needs enough rebound modulus to give the jaw muscle resistance rather than a dead squeeze.
- Labial seal. The lips flare around the wide base and close the oral cavity. Intra-oral negative pressure in this phase is commonly in the range of 10–30 kPa.
A teat that is soft everywhere fails the first requirement or the second. A teat that is firm everywhere passes neither comfortably. The engineering answer is not one hardness — it is a hardness gradient.
3. Durometer and graduated wall thickness
The most common mistake at brief stage is asking for the softest possible silicone. Push the durometer down to Shore A 25–30 and the tip collapses under suction, flow stalls, and the assembly may not survive the mechanical strength tests the destination market requires.
Upmarket designs work in a narrower band — commonly Shore A 45±2 or 50±2 — and put the softness where it is needed by varying wall thickness instead:
| Zone | Wall thickness | What it does |
|---|---|---|
| Tip (extension and peristalsis) | 0.8–1.0 mm | Deforms under light tongue pressure; internal anti-collapse ribs keep the channel open under strong suction |
| Areola transition (compression and rebound) | 1.5–2.2 mm | Gives the jaw a consistent rebound; supports a deeper latch |
| Base and vent seat (structure) | 2.8–3.5 mm | Resists distortion when the collar is tightened; gives the anti-colic valve a rigid seat |
Those figures are engineering ranges used across the category, not a specification of ours. The point is the principle: one mould, three thickness zones, one durometer.
4. Teething: tear strength and the pull test
Between four and six months the teat becomes a chew toy. If the silicone tears, the fragment is a choking hazard, and that is the failure mode regulators test for.
Two numbers matter, one at the material level and one at the finished-part level:
- Tear strength. High-purity fumed-silica LSR is normally specified at ≥35 kN/m by ASTM D624 Die B. Precipitated silica compounds cost less and tear earlier, especially at the cut edge.
- Pull resistance. The applicable drinking-equipment safety standard applies a multi-directional tensile hold of about 90 N — roughly 9 kg static load — after a simulated bite sequence. No visible crack, tear or perforation is allowed.
5. Flow stages are geometry, not just hole size
Flow rate is not a function of hole area alone. The shape of the cut, the sharpness of the cut edge, the durometer and the vent valve all sit in the same equation.
| Stage | Age | Cut geometry | How it is made | Feeding behaviour |
|---|---|---|---|---|
| S (slow) | 0–1 month | Round hole, 0.4–0.5 mm | In-mould pin or precision cold punch | Low constant flow for a swallow–breathe rhythm that is not yet coordinated |
| M (medium) | 2–3 months | Round hole, 0.7–0.8 mm | Tungsten-carbide hollow punch, vertical cold cut | Roughly 40–60% more volume per unit time |
| L (Y-cut) | 3–6 months | Three-axis Y slit at 120° | Three-blade micro die | Closes at rest, opens in proportion to suction — demand flow |
| XL (cross-cut / straw) | 6–18 months | 90° cross slit or spout/straw valve | Four-blade die plus flow check | Largest opening; handles thicker formula and purées |
6. Why durometer drift breaks both flow and venting
For a slit teat, the effective hydraulic diameter opens with suction and closes with the material's elastic modulus and wall thickness. In plain terms: flow rises with pressure, and rises sharply as the silicone gets softer or thinner.
That is why a batch that leaves the factory at Shore A 38 instead of 45 is not a cosmetic problem. At the same suction, the slit opens further and delivered flow can rise by a quarter to nearly half — enough to make a three-month-old choke. The same mechanism runs in reverse with age: after a few hundred sterilising cycles and repeated lipid contact, the silicone network relaxes, the cut edge creeps open, and the vent valve either sticks or stops sealing.
This is the engineering reason the 60–90 day replacement message is not a sales tactic. The part genuinely changes behaviour.
7. Surface texture and post-curing
Two finishing decisions separate a teat that feels like skin from one that feels like a rubber stopper.
Texture from the mould, not from a coating. Sprayed matte coatings are the wrong answer for something a baby mouths. The durable route is to cut the texture into the cavity: mirror polish on the tip (SPI A1/A2) and a controlled micro-texture on the lip-contact zone to VDI 3400 (typically VDI 18–24). The result is a velvety matte surface with lower static friction, no coating to flake, and no change after sterilising.
Post-curing. Platinum-cured LSR still carries trace low-molecular cyclic siloxanes (D4–D8) after moulding. Left in place they show up as an odour on boiling and as volatile organic matter in migration testing — the German LFGB sensory and VOM assessment is the usual gate. A 200 °C, four-hour forced-air post-cure drives them out. It is an oven-time cost, and it is the difference between passing and failing that gate.
8. Where KOBOY fits
Teats are moulded in-house, not bought in. Our LSR lines are automated, including a dedicated automated line for teats and nipples, running platinum-cured silicone. We also run 2K two-shot moulding for hard–soft assemblies, and every tool is built in our own mould shop — which is what makes iteration on a teat core practical rather than a six-week wait.
What that means in practice:
- Durometer, wall-thickness zones and cut geometry are set at the tool, so a change to the tip profile is a tool change, not a new supplier.
- Vent valves and sealing elements can be overmoulded into the base rather than added as loose parts.
- Capacity and flow rate can be matched per stage across the same teat platform.
And the limits, stated plainly:
- We do not run an in-house sensory or migration laboratory. LFGB, FDA and destination-market testing is arranged through accredited third-party labs. We can tell you what the standard requires; we cannot issue the report ourselves.
- We do not publish a fixed durometer as a catalogue promise. The right hardness depends on the teat geometry and the flow stage you are targeting, and it is agreed per project.
- The ranges in this article are engineering references, not our test data. Treat them as a starting point for a specification discussion.
9. What to put in the brief
- Target flow per stage, in ml per minute at a stated suction, rather than “slow / medium / fast”.
- The durometer band you want, and which zones should be softer.
- The destination market, so the test plan is set before the tool is cut.
- The venting architecture, because the teat base and the valve seat are one design decision, not two.
Send us the stage range and the market you are selling into — see how we run a development project, or send us the brief.