This is commonly referred to as "exudation" or "frost," and is a surface defect.

This white bloom is essentially formed when certain additives or components from within the PVC product migrate to the surface and crystallize. The main causes are as follows:

- Formulation issues (most common):

Stabilizer exudation: Heat stabilizers used to prevent PVC decomposition during processing (such as lead salts, calcium-zinc compounds), if added in excess or poorly compatible with the system, can easily exudate to the surface and form a white bloom.

- Lubricant exudation: Excessive internal or external lubricants can also migrate to the surface, forming an oily or waxy mist that appears as a white bloom upon cooling.

- Filler influence: If fillers (such as calcium carbonate) are damp or contain impurities, it can also cause surface problems.

- Processing issues:

- Excessively high processing temperature: Excessively high temperatures make additives more prone to migration.

- Uneven or insufficient cooling: If the product cools too quickly after extrusion or calendering (rapid cooling), the surface additives do not have enough time to diffuse inwards and will remain on the surface, forming a white bloom.

- Mold or roller problems: Residual exudates on the mold or roller surface can also contaminate subsequent products.

- Environmental factors:

- Humid storage environment: PVC products stored in a humid environment may absorb moisture and react with surface additives to form a white powder (especially lead salt stabilizers, which easily react with hydrogen sulfide to form white lead sulfide).

- Reaction with contacting substances: For example, storing with sulfur or certain rubber products may cause a chemical reaction that produces a white substance.

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