Condensed silicone and additive silicone are two dominant silicone polymer types, each with unique chemical compositions, curing behaviors, and performance traits. The choice between them directly impacts project costs, precision, and application suitability—whether you’re making DIY crafts, industrial molds, or medical devices. This article breaks down their differences across 7 critical dimensions, with clear comparisons, real-world examples, and selection guidelines to help you choose the right silicone for your needs.
1. Chemical Composition & Molecular Structure
The fundamental difference between the two silicones lies in their base components and molecular chains—this drives all other performance variations.
| Aspect | Condensed Silicone | Additive Silicone |
| Main Chain | Terminated dimethicone (contains active hydroxyl groups (-OH)). | Vinyl-terminated dimethicone (no active hydroxyl groups). |
| Crosslinking Agent | Methyl triethoxysilane or similar compounds (triggers condensation reactions). | Hydrogen-containing silicone oil (enables addition reactions via silicon-hydrogen bonds). |
| Catalyst | Organotin compounds (e.g., dibutyltin dilaurate). | Platinum complexes (e.g., chloroplatinic acid complexes). |
| Molecular Stability | Low—hydroxyl groups react easily with moisture in air (prone to premature curing). | High—no active groups; resistant to environmental interference (stable in storage). |
Key Impact: Additive silicone’s stable molecular structure makes it ideal for long-term storage and precision applications (e.g., medical device molds), while condensed silicone’s reactive hydroxyl groups require tight sealing to avoid waste.
2. Curing Mechanism & By-Products
How each silicone hardens and the substances it releases during curing are critical for safety and application suitability.
| Curing Trait | Condensed Silicone | Additive Silicone |
| Reaction Type | Condensation reaction (hydroxyl groups react with crosslinkers). | Addition reaction (silicon-hydrogen bonds (Si-H) react with vinyl groups (Vi)). |
| By-Products | Releases small molecules: ethanol, water, or acetic acid (acetic acid types have a mild vinegar-like odor). | No by-products—clean curing (no odor, no volatile emissions). |
| Environmental Dependence | Relies on air moisture for curing (faster in high humidity; slow or incomplete in dry environments). | No moisture dependence—curing speed depends on temperature or catalyst concentration. |
| Curing Speed Control | Hard to adjust—largely determined by humidity (e.g., 24–48 hours at 50% humidity). | Highly controllable—accelerate with heat (60°C cuts time by 50%) or higher catalyst dosage. |
Real-World Example: A DIY enthusiast making candle molds with condensed silicone finds curing takes 36 hours in a dry winter room (30% humidity), but only 20 hours in a humid summer (70% humidity). An electronics manufacturer using additive silicone for LED lens potting cures parts in 2 hours at 80°C—consistent results regardless of weather.
3. Performance Characteristics
This dimension directly affects precision, durability, and application scope—especially for industrial or high-stakes uses.
| Performance Metric | Condensed Silicone | Additive Silicone |
| Shrinkage Rate | High (1–2%)—causes minor detail distortion (not for precision parts). | Low (0.1–0.5%)—retains fine details (ideal for semiconductor molds or jewelry). |
| Hardness Range | Narrow (Shore A 20–40)—mostly soft, flexible variants. | Wide (Shore A 10–60)—adjustable for soft (e.g., medical catheters) or rigid (e.g., optical parts) needs. |
| Elongation at Break | Moderate (200–250%)—may tear under high stress. | High (300–400%)—handles stretching (e.g., flexible gaskets for machinery). |
| Corrosiveness | Acetic acid variants may corrode sensitive metals (e.g., copper, brass) or electronic components. | Non-corrosive—safe for metals, electronics, and food-contact applications. |
Critical Use Case: A dental lab cannot use condensed silicone for crown molds (1–2% shrinkage ruins fit), but additive silicone’s 0.3% shrinkage ensures perfect patient-specific replicas.
4. Application Scenarios
Their performance differences make each silicone suited to distinct use cases—matching the right type to your project avoids rework and costs.
| Category | Condensed Silicone Ideal For | Additive Silicone Ideal For |
| Cost-Sensitive Projects | Low-precision, high-volume uses: door/window sealants, ordinary craft molds, low-end electronic potting. | High-value, low-volume uses: medical device components, food-grade baking molds, precision electronic packaging. |
| Environmental Requirements | Non-critical environments: DIY workshops, outdoor sealing (resistant to moisture but not chemicals). | Strict environments: cleanrooms (no by-products), food processing (FDA compliance), medical facilities (sterilizable). |
| Precision Needs | Parts with loose tolerances (±0.5mm): toy components, decorative plaques. | Parts with tight tolerances (±0.1mm): LED lenses, semiconductor wafers, dental crowns. |
Industry Example: An automotive factory uses condensed silicone for non-critical door seals (low cost, high volume), but additive silicone for fuel system gaskets (non-corrosive, precise fit to prevent leaks).
5. Storage & Operation Precautions
Proper handling ensures shelf life and curing success—each silicone has unique requirements.
| Precaution Type | Condensed Silicone | Additive Silicone |
| Storage Conditions | – Seal tightly to block air moisture (premature curing occurs if exposed).- Shelf life: 6–12 months (unopened). | – Store away from sulfur, amines, or phosphides (poison platinum catalysts).- Avoid high temperatures/UV (denatures silicone).- Shelf life: 12–24 months (unopened). |
| Operation Safety | – Ventilate work areas (acetic acid fumes irritate airways).- Wear gloves to avoid skin contact with organotin catalysts. | – No special ventilation needed (no by-products).- Avoid contact with rubber gloves (sulfur in rubber ruins curing). |
| Substrate Preparation | Low requirements: accepts slightly oily or dusty surfaces (strong adhesion). | High requirements: substrates must be clean/dry (oils/dust block curing). |
Common Mistake: A hobbyist leaves a can of condensed silicone open overnight—moisture triggers partial curing, making it unusable. A manufacturer uses sulfur-containing lubricants near additive silicone—platinum catalyst poisoning causes incomplete hardening.
6. Cost & Availability
Cost is a key factor for budget-conscious projects—each silicone varies in material and operational expenses.
| Cost Aspect | Condensed Silicone | Additive Silicone |
| Material Cost | Low (\(10–\)20 per kg for standard grades). | High (\(30–\)60 per kg for standard grades; up to $100/kg for medical/food grades). |
| Operational Cost | Low—no special equipment (works with basic tools like spatulas). | High—may need vacuum degassing machines (for bubble-free curing) or temperature-controlled ovens. |
| Waste Rate | Higher—premature curing from moisture exposure or incorrect mixing. | Lower—stable in storage; curing failures are rare if platinum catalyst is protected. |
Cost Tradeoff: A startup making 1000 ordinary toy molds saves \(4,000 using condensed silicone (\)15/kg) instead of additive (\(40/kg). However, a bakery using additive silicone for food-grade molds avoids \)10,000 in FDA fines (condensed silicone is non-compliant).
7. Quick Selection Guide
Use this table to quickly match your project needs to the right silicone:
| Your Project Need | Choose Condensed Silicone? | Choose Additive Silicone? |
| Low cost, high volume, low precision | ✅ Yes | ❌ No |
| Food/medical contact or cleanroom use | ❌ No | ✅ Yes |
| Tight tolerances (±0.1mm) or fine details | ❌ No | ✅ Yes |
| Curing in humid environments (no oven) | ✅ Yes | ❌ No (but works, just not dependent) |
| Long-term storage (12+ months) | ❌ No | ✅ Yes |
8. Yigu Technology’s Perspective on Condensed vs. Additive Silicone
At Yigu Technology, we’ve resolved countless project failures from misselecting silicone. A common issue: clients use condensed silicone for precision electronic molds—1–2% shrinkage ruins component fit, leading to \(5,000+ in rework. We always recommend additive silicone for high-value projects (medical, electronics) despite higher costs—it eliminates shrinkage and corrosion risks. For budget projects (e.g., outdoor seals), condensed silicone is ideal, but we advise clients to seal containers tightly and test humidity levels. Our key insight: Don’t just choose based on cost—match silicone to your project’s precision, environment, and compliance needs. A \)10/kg savings on condensed silicone isn’t worth $100,000 in FDA fines for non-compliant food molds.
9. FAQ: Common Questions About Condensed & Additive Silicone
Q1: Can I use condensed silicone for food-contact projects (e.g., baking molds)?
A1: No—even non-acetic acid condensed silicones lack FDA compliance (may leach chemicals). Additive silicone is the only safe choice for food contact (look for FDA 21 CFR 177.2600 certification) as it has no by-products and meets strict purity standards.
Q2: Why does my additive silicone fail to cure even with the right ratio?
A2: Platinum catalyst poisoning is the main cause—check for contact with sulfur (rubber gloves, lubricants), amines (some adhesives), or phosphides (certain cleaning products). Replace contaminated tools/substrates and use fresh additive silicone to fix the issue.
Q3: Which silicone is better for outdoor use (e.g., garden fountain seals)?
A3: Condensed silicone is better for outdoor, non-critical seals—it’s cheaper and moisture accelerates curing (ideal for rainy environments). However, if the seal contacts drinking water or needs to withstand chemicals (e.g., pool chlorine), use additive silicone (non-corrosive, more durable).