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Date：2026-10-12How should steering wheel mould be dealt with on a car? Not by wiping the leather face alone, because the leather wrap and the foam layer underneath both need work. Treat the leather at the fatliquoring and finishing stage with iHeir-PF leather antimicrobial agent at 0.05%-0.2% on leather weight, keeping the working liquor below pH 8, and treat the inner foam with iHeir-FP foam antimicrobial agent at 0.5%-1.5% on total foam weight; the two are entirely different materials. This article covers the selection and figures for both and the humidity control at assembly and vehicle storage.
1. Two lines on a steering wheel: the leather and the inner foam
A steering wheel breaks into two layers: the leather or synthetic wrap on the outside, and the moulded foam rim and carrier inside. The materials and processes differ, so the damp takes two paths, the leather going through the surface and the foam holding moisture inside.
The leather line is the one most easily overlooked, at the fatliquoring and finishing stage. Under damp conditions and an acidic environment, chrome-tanned hides in the wet-blue state grow mould very readily, which discolours the leather, and heavy growth lowers the grade of the hide. Once the wrap is stitched onto the rim there is also an interface between leather and foam, and water trapped there brings mould just as well. The inner line: the foam rim is porous and is the layer in a steering wheel that takes up water most readily, so a rim stacked before it has fully cured keeps its water inside.
Wiping the leather therefore covers only the appearance, leaving the moisture-holding foam untouched, and that layer cannot be separated once the wheel is assembled. Both have to be handled at the moulding stage, and they take two different grades.
2. Leather wrap and inner foam at a glance
The table lines up the layer, the material, the product, the figure and the points to watch, so it can serve as the first draft of a process card.
| Layer | Material | Product | Figure | Points to watch |
|---|---|---|---|---|
| Leather wrap | Chrome-tanned leather | iHeir-PF leather antimicrobial agent | 0.05%-0.2% on leather weight | Working liquor pH 3-8; added at fatliquoring and finishing, 25KG or 200KG plastic drum |
| Inner foam rim | Polyurethane foam | iHeir-FP foam antimicrobial agent | 0.5%-1.5% on total foam weight | Clear liquid, stable across pH 1-11; added and stirred into the liquid stage, 25kg pack |
| Carrier and trim | Metal / plastic carrier | None, humidity control | Below 60% relative humidity | De-grease assembly faces; the carrier does not take up water, so the assembly environment matters |
| Vehicle storage and export packing | Cabin air and container air | None, humidity control | Below 60% relative humidity | Control the vehicle store; match desiccants to the container type for export |
One conclusion from the four rows: two rows are the dosing points, one on a leather antimicrobial agent and one on a foam antimicrobial agent, calculated on leather weight and total foam weight respectively, while the last two dose nothing and rest on the assembly environment and store humidity. Miss one of the two layers and the spending on the other is cancelled out.
3. Leather wrap: PF at the fatliquoring and finishing stage
The leather wrap takes iHeir-PF leather antimicrobial agent at 0.05%-0.2% on leather weight. PF is an emulsifiable liquid combining an active ingredient with its carriers, forming an emulsion in water, with a working liquor pH between 3 and 8 and an active content of 30±1%; added at the fatliquoring and finishing stage, it restrains microbiological damage to the wet-blue hide, protects the finished leather from degradation and keeps the grade from dropping. It ships in 25KG and 200KG plastic drums.
Three details. First, the figure is on leather weight, and hides differ in thickness and area between lots, so it is calculated on actual leather weight. Second, keep the working liquor pH under control and avoid pushing the system to the alkaline side, because crossing the range affects the treatment. Third, clean and dry the leather before wrapping so no water is left at the leather-to-foam interface, and run a small sample to confirm feel and colour before a large batch.
4. Inner foam: FP on total foam weight
The inner foam rim takes iHeir-FP foam antimicrobial agent at 0.5%-1.5% on total foam weight. FP is a clear liquid with good stability across pH 1-11 and stability to light and heat; the loading is small and the activity high, with a peak antimicrobial rate reaching 99.99%, a skin irritation score of zero and a sensitisation rate of zero, shipped in 25kg packs.
Three details. First, the figure is on total foam weight, so a change to the pour formulation means recalculating. Second, FP has to be stirred evenly through the other components, because uneven concentration brings uneven cure and shows up in the feel and dimensions of the rim. Third, allow enough cure time before stacking, and do not press uncured rims together. For the differences between foams and other elastomers, the logic is set out in antimicrobial treatment for foams and elastomers.
5. Assembly and vehicle storage: two jobs, humidity and cleaning
Assembly and storage dose nothing and rest on the environment. Hold the assembly line below 60% relative humidity and clean benches and totes on a schedule. Once a wheel is fitted to the body the cabin becomes a sealed pocket and a day-to-night swing condenses on the inner faces first, so the vehicle store needs humidity control too, and freshly built vehicles should not be parked in the open or against a cold wall.
Export adds another layer: a container swings far more than a warehouse, condensate runs down the container wall, and the first to get wet are the vehicles and parts stacked against it. Match desiccants to the container type to hold the container air and wall condensate. For batches that have already gone mouldy, the order of rework is set out in mould treatment for car interiors.
6. Questions that come up: wiping the leather, and choosing for it
Is wiping the leather face enough on a mouldy steering wheel? No. The leather is dense and does not take up water, while the foam inside is the layer that holds moisture; with the leather alone, water at the interface still brings mould from within, where it cannot be seen and cannot be reached once assembled.
What decides the leather grade? The usable pH range and process compatibility. Leather is treated at the fatliquoring and finishing stage, so choose a grade that is stable from acidic to neutral and is carried into the fibre with the working liquor, and calculate the figure on leather weight; confirm feel and colour on a small sample.
With the compound in, is humidity control still needed? Yes. The compound covers the leather and the foam themselves, while the assembly environment and the vehicle store are outside its reach, and both cabin condensate and container condensate are handled by humidity control and desiccants.
Two dosing points carry the work: the leather wrap takes iHeir-PF leather antimicrobial agent at 0.05%-0.2% on leather weight at the fatliquoring and finishing stage with the working liquor kept below pH 8, and the inner foam takes iHeir-FP foam antimicrobial agent at 0.5%-1.5% on total foam weight, stable across pH 1-11, stirred into the liquid stage; assembly and vehicle storage hold the result through humidity control and cleaning. Samples and TDS sheets are available to run a trial against your hides and material systems.
