Walk into any hardware store or construction site, and you’ll see rows of tubes labeled with unfamiliar terms. Silicone. Polyurethane. Butyl. For many, choosing the right one feels like guesswork. But sealants aren’t one-size-fits-all. Each category is designed with specific materials, environments, and performance goals in mind. Understanding how they differ starts with breaking down the main families.

Sealants fall into several core categories: silicone, polyurethane, polysulfide, butyl, and acrylic. These are defined not just by what they stick to, but by their base chemical formulation. That base controls everything—durability, flexibility, resistance to weather or chemicals, and application method.

Silicone Sealants: Versatility and Performance

Silicone sealants are very useful in construction. Of all the types, they offer great flexibility and are very resistant to weather. They handle movement better than most other sealants, and this is important where expansion and contraction happen frequently.

There are two main types: acetoxy-cure and neutral-cure (also called oxime or alkoxy). The difference is in the way they harden. Acetoxy formulas release acetic acid as they cure—you can smell a vinegar odor. These types tend to cure faster and work well on non-porous surfaces such as glass or ceramic. Neutral-cure versions release alcohol or a similar substance instead, so they are gentler on sensitive materials like metal or concrete.

Silicone remains flexible from -50°C to 150°C, so this means it performs well in both very cold and very hot temperatures. It doesn’t shrink or crack easily. UV rays are not a problem. And it also resists ozone and most weathering effects for many years.

Common uses include exterior joints, window frames, siding, and any place with constant temperature changes. In bathrooms and kitchens, it seals around sinks and tubs because it handles humidity without failing. Special types are made for cleanroom or medical uses.

Structural Sealants for Building Applications

When glass holds up an entire wall, it’s about more than just sealing a small space. Structural sealants are used where things support weight, particularly in curtain walls and glass building fronts. These aren't just for looks or secondary—they’re doing very important work.

Most are silicone-based formulas with one or two components. One-component products are easier to use, but they are slower to cure. Two-component systems are mixed at the nozzle or with special tools, curing much faster and providing higher strength.

These sealants bond glass, metal, or panels made of mixed materials to structural frames. They absorb building movement and, at the same time, hold panels firmly in position. The best kinds balance strong bonding, flexibility, and lasting use.

How well they work depends on the right joint design, cleaning the surfaces well, and applying them carefully.

Primary and Secondary Sealants for Insulating Glass

Insulating glass units (IGUs) use a dual-seal system to keep heat, cold, and moisture out. That system includes a primary seal, usually made from butyl, and a secondary seal, often silicone or polysulfide.

The primary seal bonds directly to the spacer bar between the glass panes. Its main job is to block moisture vapor transmission and stop gases (like argon or krypton) from leaking out. Butyl works well here because of its low gas permeability and strong adhesion to glass and aluminum.

The secondary seal wraps around the outside, providing structural strength and additional moisture protection. Silicone works well for its weathering and UV resistance. Polysulfide is chosen when chemical exposure or fuel resistance is a factor.

This two-layer system helps IGUs last for years, even in tough climates. It protects the insulating gas inside and prevents condensation or fogging between the panes.

Butyl Sealants: Properties and Applications

For situations where moisture control is critical, butyl sealants come into play. Most often used as a primary seal in insulating glass, they are applied hot and form a strong, flexible bond.

The core ingredient is polyisobutylene, a synthetic rubber with low gas and moisture permeability. Once applied, butyl stays pliable and sticky without hardening or cracking over time.

Performance ranges from -30°C to 80°C, which covers most indoor and moderate outdoor conditions. Butyl adheres well to both glass and metal, especially aluminum. It doesn’t do well under direct UV light, so it usually goes beneath a secondary layer in window systems or inside joints that won’t see sunlight.

Beyond glass, it’s sometimes used in roofing or metal panels where sealing overlaps or preventing vapor intrusion is key. It isn’t suitable for places with wide joint movement because of limited elasticity, but for static seals, it works extremely well.

Primary and Secondary Sealants for Insulating Glass

Insulating glass units (IGUs) use a two-seal system to keep heat, cold, and moisture out. That system includes a primary seal, usually made of butyl, and a secondary seal, often silicone or polysulfide.

The primary seal bonds right to the spacer bar between the glass panes. Its main job is to block water vapor and stop gases (like argon or krypton) from leaking out. Butyl works well here because it has very low gas permeability and strong sticking power to glass and aluminum.

The secondary seal wraps around the outside edge, so it provides structural strength and extra moisture protection. Silicone works well for this because it is resistant to weather and UV light. Polysulfide is chosen when resistance to chemicals or fuel is needed.

This two-part system helps IGUs last for many years, even in harsh weather. It protects the insulating gas inside and prevents fog or condensation between the glass panes.

Butyl Sealants: Properties and Applications

For situations where controlling moisture is very important, butyl sealants are useful. Most often used as a primary seal in insulating glass, they are applied hot and form a strong, flexible bond.

The key ingredient is polyisobutylene, a synthetic rubber with low gas and moisture permeability. Once applied, butyl stays pliable and sticky without hardening or cracking as time passes.

Performance ranges from -30°C to 80°C, so this covers most indoor and moderate outdoor conditions. Butyl adheres well to both glass and metal, especially aluminum. It doesn’t do well under direct UV rays, so it usually goes beneath a secondary layer in window systems or inside joints that won’t be exposed to sunlight.

Beyond insulating glass, it’s sometimes used in roofing or metal panel systems where sealing overlaps or preventing vapor from getting in is important. It isn’t suitable for areas with a lot of joint movement because of its limited stretchiness, but for static seals, it performs very well.

Acetoxy Silicone for Specific Applications

Where speed matters, acetoxy-cure silicone offers an edge. It hardens quickly, forming a durable, flexible seal in hours instead of days.

These sealants work best on non-porous surfaces like tile, glass, and enamel. That’s why they’re used in kitchens, bathrooms, aquariums, and clean rooms. Many are available in clear or translucent finishes, offering a clean, finished look.

However, acetoxy silicone reacts poorly with some materials. It can corrode concrete, marble, and certain metals like copper or galvanized steel. That limits its use in structural or exterior applications.

Still, where compatibility isn’t an issue and appearance matters, acetoxy silicone remains a reliable, quick-setting option.

Temperature Considerations in Sealant Selection

Sealants behave differently under hot or cold conditions. Some become brittle in winter. Others sag in high heat. So, temperature performance should match the expected environment.

Silicone handles the widest range—from -50°C to 150°C—without losing flexibility. So, that makes it ideal for outdoor or industrial settings. Butyl handles moderate temperature changes, but it can soften in extreme heat. Polysulfide maintains flexibility through weather cycles, and it has good resistance to getting old from heat. Polyurethane is strong, but it may harden or break down with long-term sun or high-heat exposure.

Thermal cycling is another important factor. Expansion and contraction stress the bond again and again. Sealants that stay flexible without losing their stickiness perform best here. Cold climates need elasticity at temperatures below zero. Hot regions need materials that don’t soften or drip in the sun.

Surface Preparation and Application Best Practices

No matter how good the sealant is, poor preparation will ruin the job. The application starts with surfaces that are clean, dry, and structurally sound. Dust, oil, old sealant, or moisture all reduce how well it sticks.

Use lint-free cloths, the correct solvents, and mechanical abrasion if needed. Some materials require primers, especially when bonding to porous surfaces or surfaces resistant to chemicals. Always test a small area before doing the full application.

Backer rods or bond-breaker tapes help control the depth and shape of the joint. This helps with correct movement and avoids sticking on three sides because that can cause cracking.

Apply the sealant with a steady hand, smooth the surface with a tool or finger, and allow the right amount of time for curing. Keep the area protected during that time, especially from rain, dust, or movement.