Dip Molding
Dip molding withdraws a heated former from liquid plastisol or latex, leaving a coating that cures into a flexible open-ended part such as a grip or cap.
- Part
- Forming
- Revised
- 2026-08-11
At a glance
- Family
- Plastics and Rubber
- Typical tolerances
- Inside diameter follows the former closely, about ±0.005 in (±0.13 mm); wall thickness is much looser at roughly ±0.010–0.030 in (±0.25–0.75 mm) and varies along the dip axis.
- Surface finish
- The inside surface reproduces the former's machined finish; the outside is a smooth, self-leveled gloss from drainage
- Typical volumes
- 100 to several million parts; economical at both ends because tooling is so inexpensive
- Lead time
- 1–3 weeks for formers; hours per rack thereafter, with cycle time driven by fusion oven residence
- Materials
- Plastic
What it is
Dip molding immerses a heated metal former in liquid PVC plastisol, latex, or polyurethane dispersion, holds it long enough for a layer to gel against the hot surface, then withdraws and fuses the coating in an oven. The cured part is stripped off the former, so every dip molded part is open at one end — grips, handle covers, end caps, plugs, protective boots, gloves, and dip-coated tool handles.
Tooling is the cheapest in plastics: a former is a machined or cast metal shape with no cavity, no parting line, and no clamp requirement. Add more formers to a rack and you have added cavitation. That combination makes dip molding economical from a few hundred parts, and it stays economical into the millions.
Wall thickness is set by former temperature and dwell time rather than by a mold, and typically lands between 0.020 and 0.125 in (0.5–3 mm).
How it works
- Heat the former. Formers are preheated in an oven, typically to 300–400 °F (150–205 °C) for PVC plastisol. Former temperature and its thermal mass are the primary controls on how much material gels, which is why formers are made from solid aluminum or steel rather than thin shells.
- Dip. The hot former is lowered into a tank of plastisol — a suspension of PVC resin particles in liquid plasticizer — at a controlled rate. Dipping too fast entrains air; too slow leaves witness rings at each pause.
- Dwell. Heat conducts from the former into the surrounding liquid and the PVC particles swell and gel into a soft solid layer. The layer builds quickly at first and then more slowly, because the gelled material insulates the former and the former is cooling. Dwell time is the main operator control on wall thickness.
- Withdraw and drain. The former is lifted out and the excess drains back to the tank. Drainage during withdrawal is why dip molded parts are not perfectly uniform in wall thickness along the dip axis. Parts are often rotated or inverted during this phase to even out the distribution.
- Fuse. The coated former passes through an oven at roughly 350–400 °F (175–205 °C) until the plastisol fully fuses, going from a soft gel to a tough, clear-to-opaque elastomer. Under-fusing leaves a weak, chalky part that tears easily; over-fusing discolors it.
- Cool and strip. After a water quench or air cool, the part is peeled off the former, usually with compressed air introduced between part and former. Draft and the material's elongation are what make this possible.
How does latex dipping differ?
Natural rubber latex is coagulant-dipped instead of heat-gelled: the former is first dipped in a coagulant salt solution, then in latex, where the coagulant destabilizes the emulsion at the surface. It runs near room temperature and is the route for gloves and thin-wall medical parts.
Design guidelines
Shape
The former has to come out, so the part must be open at one end and free of internal undercuts that would trap it. Draft of 1–2° per side makes stripping cleaner, though the elastomer's elongation lets you get away with less on soft compounds. Closed hollow shapes are impossible.
Wall thickness
0.020–0.125 in (0.5–3 mm) is the practical range, with 0.040–0.080 in (1.0–2.0 mm) the most common. Thicker builds need longer dwell or repeated dips, which stretches the cycle. Expect real variation along the dip axis from drainage — design so a nominal-plus-or-minus wall is acceptable, and put any sealing or press-fit function on the inside diameter.
Which dimension can you actually control?
The inside surface is formed against the machined former, so it reproduces it closely — this is where interference fits, retention beads, and location features belong. The outside surface is free-formed by drainage and surface tension, so it is the loose dimension. Getting this the right way round is the single most important decision in a dip molded part.
Corners and edges
Radius everything. Sharp external corners on the former cause the gelled layer to thin as it drains and can leave a weak spot; sharp internal corners collect material and cure unevenly. A radius of at least one wall thickness is the floor.
Features you can and cannot have
Retention beads, internal ribs, and grip textures on the inside surface all come free, because they are machined into the former. Text and logos can be engraved into the former and read through as raised detail. What you cannot have is a controlled outside profile, a closed end with a controlled internal void, or a sharp lip — the open end always finishes with a slightly rounded, drained edge unless it is trimmed.
Former material
Aluminum heats and cools quickly and shortens the cycle; steel holds heat longer, which favors thicker builds and larger parts. Both machine easily and neither sees any pressure, which is why formers cost so little compared with any cavity tool — see /charts/material-properties for the density and conductivity trade behind that choice.
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Wall thickness | 0.040–0.080 in (1.0–2.0 mm) | 0.020–0.125 in (0.5–3 mm) | Thicker builds need repeated dips |
| Draft | 1–2° per side | About 0° on soft compounds | The former has to strip out |
| Controlled surface | Inside diameter | — | Formed directly against the machined former |
| Free surface | Outside profile | — | Set by drainage and surface tension |
| Radius | ≥ 1 × wall thickness | — | Sharp corners drain thin and cure unevenly |
| Geometry | Open at one end | No closed hollows | The former must be withdrawn |
| Hardness (PVC plastisol) | 40–90 Shore A | — | Set by plasticizer content in the compound |
Cost drivers
Dip molding has the lowest tooling cost of any plastics process that produces a three-dimensional part. A former is a solid machined or cast shape with no cavity, no parting line, no ejection, and no pressure containment. Adding capacity means adding formers to the rack, so cavitation scales linearly and cheaply rather than in expensive multiples of a mold base.
The recurring costs are material, oven time, and labor at the strip station. Cycle time is dominated by heating the formers and fusing the coating, and it grows with wall thickness.
Volume breakpoints:
- Under 100 parts: a single machined former, hand-dipped. Viable for prototypes at very low tooling cost.
- 100–10,000: a rack of formers on a manual or semi-automatic line.
- Over 10,000: automated dip lines with multi-former racks, in-line fusion ovens, and automated stripping — the configuration behind commodity grips and caps.
Cost reduction:
- Thin the wall. Material and dwell time both scale with it, and dwell time drives the cycle.
- Add formers, not shifts. Formers are cheap; oven and tank capacity are the constraint, so fill the rack.
- Put functional features on the inside. They are machined into the former once and reproduce free on every part, replacing secondary operations.
- Choose a color in the plastisol. Compound is pigmented in the tank, so color is nearly free, whereas painting a flexible part is expensive and prone to cracking.
- Accept a drained open edge. Specifying a trimmed, square lip adds a secondary operation to every part for what is often a cosmetic preference.
Questions
6 questionsWhat wall thickness can dip molding achieve?
Typically 0.020–0.125 in (0.5–3 mm), with 0.040–0.080 in (1.0–2.0 mm) most common. Thickness is controlled by former temperature and dwell time rather than by a mold cavity, and thicker builds need longer dwell or repeated dips, which lengthens the cycle.
Which surface of a dip molded part is dimensionally accurate?
The inside. It forms directly against the machined former and holds roughly ±0.005 in (±0.13 mm), so interference fits, retention beads, and locating features belong there. The outside profile is free-formed by drainage and surface tension and is much looser — typically ±0.010–0.030 in (±0.25–0.75 mm) on wall.
Why must dip molded parts be open at one end?
Because the former has to be withdrawn from the finished part. There is no split mold, so any geometry that would trap the former — a closed hollow, an internal undercut — is impossible. Draft of 1–2° makes stripping cleaner, though soft compounds tolerate very little.
Why is dip molding tooling so cheap?
A former is a solid machined or cast shape with no cavity, no parting line, no ejection system, and no pressure to contain. Capacity scales by adding more formers to a rack rather than by building a multi-cavity mold, so both the entry cost and the cost of increasing output are far below any cavity-molding process.
What is the difference between dip molding and dip coating?
Mechanically nothing — the same tank, heat, and dwell. The distinction is what comes off the former. In dip molding the coating is stripped and becomes the part; in dip coating the substrate stays inside and the coating is a permanent covering, as on a plier handle or a wire-formed rack.
How is latex dipping different from plastisol dipping?
Latex is coagulant-dipped rather than heat-gelled. The former is dipped first in a coagulant salt solution and then in the latex, where the coagulant destabilizes the emulsion at the surface. It runs near room temperature instead of 300–400 °F and is the route used for gloves and thin-walled medical parts.