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When purchasing fumed silica, checking only the silica content or BET surface area is not enough.
For silicone rubber, sealants, adhesives, coatings, and other industrial formulations, actual performance can also be influenced by moisture, pH, sieve residue, tamped density, surface characteristics, and dispersion.
The purpose of reviewing a COA is therefore not simply to check whether each number is within specification.
A more useful question is:
Does this batch of fumed silica match the existing formulation and process, and can the supplier maintain consistent quality from batch to batch?
BET specific surface area is one of the basic parameters used to classify fumed silica.
Changes in surface area can affect the interaction between silica and the formulation, influencing thickening, thixotropy, reinforcement, and dispersion requirements.
However, a higher BET value does not automatically mean better performance.
Higher surface area may provide stronger surface interaction, but it can also increase dispersion difficulty and cause a greater increase in formulation viscosity.
For an established formulation, consistency and compatibility are often more important than simply choosing the highest surface area available.
Loss on drying provides useful information about moisture and volatile content in the material.
In moisture-sensitive adhesives, sealants, and other formulations, changes in raw-material moisture may influence storage stability, processing behavior, or final product performance.
When qualifying a new supplier or checking a new batch, loss on drying should therefore be reviewed together with BET surface area.
pH is another common parameter listed on fumed silica COAs.
Different formulation systems have different sensitivities to acidic or alkaline conditions. This can become particularly important when catalysts, curing agents, or other reactive ingredients are involved.
A pH value within specification does not automatically guarantee identical behavior in every formulation.
For an established system, parallel testing against the current material is recommended.
Fumed silica is an extremely fine powder, but larger particles or agglomerates may still occur during production, storage, transportation, or handling.
Sieve residue provides one reference for evaluating the presence of larger particles.
This may be particularly relevant in formulations where surface quality, transparency, fine coatings, or good dispersion are important.
However, a low sieve residue on the COA does not guarantee perfect dispersion in the customer's formulation.
Actual dispersion also depends on equipment, shear conditions, addition sequence, and formulation viscosity.
Silica content is an important basic indication of product purity, but it does not determine application performance by itself.
Two fumed silica products with similar SiO₂ content may still behave differently because of differences in surface area, moisture, surface chemistry, or dispersion behavior.
Therefore, purchasing decisions should not be based only on:
“Which product has the higher purity?”
A better question is:
“Which product provides the required performance with more consistent batch quality in my formulation?”
Tamped density reflects the packing condition of the powder under defined test conditions.
It can influence packaging volume, transportation, feeding, and production handling.
For long-term purchasing, significant changes in tamped density between batches can also be useful information when evaluating product consistency.
COA review is only the first stage of raw-material qualification.
For silicone rubber, sealant, adhesive, and coating manufacturers, a more practical validation process is:
COA comparison → Sample testing → Parallel formulation trial → Finished-product testing → Batch consistency verification
When changing suppliers, similar specifications alone should not be treated as proof of direct replacement.
IOTA HL7200 is a hydrophilic fumed silica with a BET specific surface area in the approximately 200 m²/g range.
It is designed for applications including coatings, HTV and RTV silicone rubber, adhesives, and sealants.
For customers already using a similar 200 m²/g hydrophilic fumed silica, HL7200 can be evaluated as a candidate through COA comparison and formulation testing.
Direct replacement should be confirmed using the customer's own formulation, processing conditions, and finished-product performance requirements.
No. BET is important, but moisture, pH, sieve residue, purity, tamped density, and actual formulation performance should also be considered.
Not necessarily. Similar BET values do not guarantee identical surface characteristics, moisture levels, dispersion behavior, or formulation performance.
A COA describes standard raw-material parameters. Actual application performance also depends on dispersion equipment, shear conditions, addition sequence, formulation composition, and interactions with other raw materials.
In addition to comparing specifications, the new material should be tested for viscosity, thixotropy, dispersion, mechanical properties, or other finished-product parameters relevant to the application.
HL7200 is a hydrophilic fumed silica that can be evaluated for coatings, HTV and RTV silicone rubber, adhesives, sealants, and related industrial formulations.
Product Reference: IOTA HL7200 Hydrophilic Fumed Silica
Final material selection should be confirmed according to the latest technical data, the customer's formulation, processing conditions, and application testing.
