On Cloudmonster 2 'Undyed / Flame' (3ME10121527) — Natural-Fiber Maximum Cushioning, No Dye Process

What Is the On Cloudmonster 2 ‘Undyed / Flame’?

The On Cloudmonster 2 ‘Undyed / Flame’ (Style Code: 3ME10121527) is the Cloudmonster 2’s most materially honest version — the same second-generation maximum-cushioning platform as the Cloudmonster 2 ‘Ivory / Silver / Red’, built with an upper that has not been dyed. Undyed is not a colorway in the conventional sense. It is a manufacturing decision: the fibers of the upper retain the color they were before the industry’s standard transformation process, the color of the raw material itself rather than the color applied to it afterward. Flame is what those natural fibers are — the orange-red warmth that exists in certain fiber types before chemical treatment, achieved not by adding color to the material but by selecting the material for the color it already has. The result is a shoe that most footwear manufacturers would not attempt: the visual energy of flame-orange, without the dye process that flame-orange would conventionally require. At $169, the Cloudmonster 2 Undyed / Flame is $30 above the dyed Cloudmonster 2 ‘Ivory / Silver / Red’ ($139) — a price differential that reflects the material selection cost of undyed construction, where color cannot be corrected after the fact and every fiber must be right before the shoe is built, not after. The platform is identical: double-layer CloudTec®, Gen 2 Helion™, Speedboard®, Gen 2 engineered mesh upper. What is different is the process — and what that process reveals about the material. US M7–M11 / W8.5–W12.5 / EU 40–45.

Quick Facts

• Brand: On Running (Zurich, Switzerland — est. 2010)
• Model: Cloudmonster 2 Undyed — second-generation maximum cushioning with natural-fiber upper
• Style Code: 3ME10121527
• Colorway: Undyed / Flame — natural fiber orange-red upper; no chemical dye process
• Construction: Undyed upper — fibers retain natural color; eliminates dyeing’s water, chemical, and energy inputs
• CloudTec®: Double-layer, training-tuned — Cloudmonster maximum cushioning, second-generation pod geometry
• Helion™: Second-generation superfoam — improved high-mileage durability
• Speedboard®: Training-calibrated — forward momentum across all training paces
• Upper: Gen 2 undyed engineered mesh — lighter + more breathable than Cloudmonster 1; natural color variation between pairs
• Gender: Men’s / Unisex sizing
• Sizing: US M7–M11 / W8.5–W12.5 / EU 40–45
• Price: $169
• Category: Road Running / Maximum Cushioning / Natural-Fiber Construction
• Fit: True to size

Specs & Technologies

What ‘Undyed’ Means — The Process That Is Not There

Conventional textile dyeing is one of the most resource-intensive steps in footwear manufacturing. A standard dye process for engineered mesh requires: significant volumes of water as the dye carrier and rinse medium (industry estimates place textile dyeing at roughly 100–150 litres of water per kilogram of fabric dyed); chemical fixatives — mordants and binding agents that bond the dye molecules to the fiber and prevent colour from washing out in use; heat energy to drive the dye into the fiber structure and to set the fixatives; and wastewater treatment before discharge, because dye effluent contains heavy metals, synthetic organics, and pH-modifying compounds that cannot be released untreated into water systems. The dye process also adds processing time and logistics between fiber production and upper construction, and it introduces the possibility of dye lot variation — the slight colour differences between production runs that dyed goods must be batch-matched to eliminate.

Undyed construction eliminates all of this. The fibers arrive at the upper construction stage in their natural state, are formed into the engineered mesh, and become the shoe without any intermediate chemical colour treatment. The environmental inputs eliminated are real and measurable: no dye-process water, no fixatives, no dye energy, no wastewater treatment. What remains is the colour the fiber already had — which, for the fibers selected for the Cloudmonster 2 Undyed / Flame, is the warm orange-red of the raw material’s natural pigmentation.

Why Undyed Construction Requires More Precise Material Selection

Conventional dyeing is, among other things, a correction tool. If a fiber batch arrives in an inconsistent natural colour, the dye process normalises it: every fibre emerges from the dye bath in the same specified colour, regardless of what colour it was before. This correction capacity means that dyed construction can tolerate significant variation in incoming fiber natural colour, because the dye will override whatever is there.

Undyed construction has no such override. The colour of the finished shoe is the colour of the incoming fiber — which means the fiber must be right before the shoe is built, not after. For the Cloudmonster 2 Undyed / Flame, this requires material selection at a precision level that dyed construction does not: each fiber batch must be assessed for its natural colour range, its consistency within the batch, and its compatibility with adjacent batches used in the same upper. Fibers that fall outside the acceptable natural colour range for ‘Flame’ cannot be corrected; they are not used. This selection precision — applied before any manufacturing begins — is the primary reason the Cloudmonster 2 Undyed / Flame is $30 above the dyed Cloudmonster 2 ‘Ivory / Silver / Red’. The platform is the same; the material sourcing is more exacting.

Natural Color Variation — Why No Two Pairs Are Identical

Natural fibers vary in colour between batches, between growing seasons (for plant-derived fibres), and even within a single batch, because the colour of a natural fiber is the result of its biological origin — the specific mineral content of the soil, the amount of rainfall in the growing season, the temperature during fibre development, the point in the plant’s growth cycle when the fiber was harvested. These variables produce colour that is consistent within a range but not identical across every unit. When dye is applied, these variations are overridden and every unit emerges in the same specified colour. When no dye is applied, the natural variation is present in the finished shoe.

For the Cloudmonster 2 Undyed / Flame, this means that two pairs of the same size may have slightly different intensities of orange-red in the upper mesh — one pair slightly warmer, another slightly more muted, both within the Flame range but not identical. This variation is not a quality defect and is not grounds for return. It is the physical evidence of the undyed construction method: the colour you see is the colour the fiber grew into, not the colour a dye bath was specified to produce. Each pair is, in this specific sense, unique — the record of the particular material that built it.

‘Flame’ — The Color the Material Already Was

Flame as a colour descriptor typically refers to the orange-red of combustion — the spectrum of colour produced when carbon-containing materials oxidise rapidly, releasing energy as light across the orange-red-yellow range. In conventional footwear, a Flame colourway would be produced by selecting a dye within that orange-red range and applying it to a neutral or white base fiber. In the Cloudmonster 2 Undyed / Flame, the process is inverted: the fibers are selected because their natural pigmentation falls within the orange-red range that ‘Flame’ describes, and the name describes what the material is rather than what has been done to it. The colour exists in the fiber’s molecular structure — the specific organic compounds and mineral interactions that produce orange-red pigmentation in natural fibres — before On Running or any manufacturer has touched it. Flame, here, is not a description of an action (dyeing) but of a state (being). The shoe is the colour of the material. The material is flame.

Cloudmonster 2 ‘Undyed / Flame’ vs. Cloudmonster 2 ‘Ivory / Silver / Red’ Women’s — Same Platform, Different Construction

Decision rule: same maximum-cushioning platform, two construction philosophies at a $30 difference. Undyed / Flame — for the runner who wants the material’s natural colour and accepts the variation that comes with it. Ivory / Silver / Red Women’s — for the women’s-specific fit and the three-colour dyed palette at standard construction cost.

Sizing — Men’s / Women’s / EU Conversion Table

The On Cloudmonster 2 Undyed / Flame is sold in men’s / unisex sizing. Women typically size up approximately 1.5 sizes from their women’s US size (e.g., women’s US 7 → men’s US 8.5 / EU 42). True to size for most runners.

Who Is the On Cloudmonster 2 ‘Undyed / Flame’ For?

Three profiles: the material-honest runner who wants On’s maximum-cushioning platform in the construction that reveals rather than conceals its source material — the Undyed / Flame’s natural orange-red is the colour the fiber grew into before any manufacturing decision was made about it, carried by a shoe that eliminated the dye process’s water, chemical, and energy inputs to show it, at $169 as $30 above the dyed version because undyed material selection has no correction step and therefore must be exact before production begins; the natural-variation buyer who wants a pair that is, in a specific and material sense, unique — no two Undyed / Flame pairs are identical in the way that dyed shoes are identical, because the natural colour of the selected fibres varies in ways that dye cannot, and each pair carries the particular material history of the fibres that built it; and the Flame palette buyer who wants the colour of fire achieved without the process that colour conventionally requires — orange-red that exists in the molecular structure of the material rather than in the dye bath it was not sent through, the most direct path between the colour and its source that footwear manufacturing currently allows.

Frequently Asked Questions

Q: What is the style code?
A: 3ME10121527.

Q: What does ‘Undyed’ mean exactly?
A: The upper fibers have not been chemically dyed. They retain the natural colour of the raw material — the orange-red that exists in the fiber’s molecular structure before any manufacturing process. The colour is the material’s own, not a colour applied to it.

Q: Why is the Undyed / Flame $30 more than the Cloudmonster 2 ‘Ivory / Silver / Red’?
A: Material selection cost. Conventional dyeing corrects fiber colour variation — if incoming fibers are inconsistent, the dye process normalises them. Undyed construction has no correction step: every fiber must be within the acceptable natural Flame colour range before the shoe is built. This pre-production selection precision costs more than standard dyed construction. The platform (CloudTec®, Helion™, Speedboard®) is identical.

Q: Will my pair look exactly like the product images?
A: Within the Flame range, yes. But no two Undyed / Flame pairs are identical: natural fiber colour varies between batches due to biological variables in the source material. Your pair may be slightly warmer or slightly more muted than another pair within the same colourway. This is natural variation, not a defect — it is the physical evidence of the undyed construction.

Q: Can I return the shoe because of colour variation?
A: Colour variation within the natural Flame range is an inherent characteristic of undyed construction, not a manufacturing defect. Each pair is assessed to be within the acceptable natural colour range for this colourway before shipment.

Q: What is the difference between this and the Cloudmonster 2 Women’s ‘Ivory / Silver / Red’?
A: Same Cloudmonster 2 platform; two differences: (1) construction — Undyed / Flame uses natural fiber colour without dye; Ivory / Silver / Red uses standard dye process; (2) fit — Undyed / Flame is men’s/unisex last; Ivory / Silver / Red is women’s-specific last. Price: $169 vs $139, reflecting undyed material selection cost.

Q: How does women’s sizing work?
A: Women size up approximately 1.5 sizes from their women’s US size (e.g., women’s US 7 → men’s US 8.5). If you prefer a women’s-specific last with narrower heel and wider forefoot geometry, the Cloudmonster 2 ‘Ivory / Silver / Red’ Women’s ($139) is built on that last.