PVB vs. SentryGlas. Which laminated glass is better?

What an interlayer is.

Impact glass is laminated glass: two lites of glass bonded under heat and pressure to a plastic layer in the middle. That middle layer is the interlayer. When a missile or debris hits, the glass may crack, but the interlayer absorbs energy, resists penetration and keeps the broken pieces bonded in place. That keeps wind and rain out of the house and stops flying shards. Two interlayers dominate Florida impact windows. PVB (polyvinyl butyral) is the long-standing, flexible film used in most laminated glass. SentryGlas is an ionoplast interlayer, often called SGP, developed in 1998 for the hurricane impact market after Hurricane Andrew. Kuraray makes both SentryGlas and Trosifol PVB; Eastman makes Saflex PVB.

• Typical large-missile laminate: two lites of heat-strengthened (HS) glass with a 0.090 in. (90 mil) interlayer.
• Thinner interlayers, such as 35 mil, are used in small-missile systems.

Stiffness and strength.

This is the biggest difference. SentryGlas is up to 100 times stiffer and five times more tear resistant than conventional PVB. Because it is so stiff, it transfers load almost perfectly between the two lites, so the laminate behaves more like one thick piece of glass. Under the same load, a SentryGlas laminate bends less. Heat matters too. For short-duration loads, PVB laminates lose strength compared with solid glass of the same thickness above about 68 °F (20 °C), while SentryGlas laminates are insensitive up to about 122 °F (50 °C). On a hot Florida wall in a storm, that stiffness is what lets the glass carry higher pressure.

Post-breakage behavior.

Every impact laminate is tested broken. After the missile hits, the whole window goes through thousands of positive and negative pressure cycles that simulate a hurricane approaching and leaving. The cracked glass has to stay in the frame. A soft PVB laminate tends to sag and pull out of the frame, so PVB systems are usually wet glazed: silicone bonds the glass edge to the frame. SentryGlas laminates stay rigid after breakage and resist pull-out during cycling. That is why SentryGlas is the interlayer recommended for dry-glazed systems, where the glass is held by gaskets and the frame instead of structural silicone.

Clarity and edge stability.

Clarity is measured with the Yellowness Index (YID). SentryGlas starts at a YID of 1.5 or less; PVB alternatives run about 6 to 12. Over the years, PVB can give glass a slightly greenish tint, while SentryGlas holds its clarity and is less vulnerable to moisture. Edge stability is a laminate's resistance to small bubbles, cloudiness or delamination along its edges. Open-edge SentryGlas samples have been weathering outdoors in Florida since 1997 and showed no visible moisture intrusion or delamination after 20 years. In a window the glass edge sits inside the frame and sealant, so PVB performs well in normal service; the difference shows most on exposed edges and over very long lives.

Why SentryGlas reaches higher pressures and larger sizes.

Design pressure (DP), in pounds per square foot (psf), is the wind load an approved window can resist. A stiff interlayer lets the same glass resist more load, span a larger opening or use thinner glass. For a large-missile laminate of 1/4 in. HS glass, a 0.090 in. interlayer and 1/4 in. HS glass, Kuraray's hurricane design charts top out at 80 psf with PVB and 170 psf with SentryGlas. Those charts are for the glass alone. A window's real rating comes from testing the complete unit, frame, anchors and all, so the approval drawing for each product sets the numbers.

How it shows up in our brands' approvals.

Florida Product Approvals list each glass build with its own sizes and pressures. In the Mr. Glass, GIG and Eurocraft approvals, the same frame often carries a much higher rating with SentryGlas than with PVB. LMI means large-missile impact. The rating always belongs to a specific glass build, size, configuration and anchorage on the approval drawing, so two windows that look alike can be rated very differently.

• Mr. Glass MG-200 single-hung, Florida FL20352-R4: on the LMI drawing, 7/16 in. SentryGlas and its insulated version reach +80/−140 psf on most sizes (lower on some of the largest); the 5/16 in. PVB glass is limited to +80/−80 psf.
• Mr. Glass MG-300 horizontal roller, Florida FL20359-R5: the 5/16 in. and 7/16 in. PVB glass is limited to +80/−80 psf; only the 7/16 in. SentryGlas glass (and its insulated version) reaches +90/−140 psf, and lower on large sizes.
• Mr. Glass MG-400 fixed window: ±100 psf (PVB glass ±65).
• GIG S-20000 single-hung: up to +120/-150 psf at the full 53-1/8 x 74-1/4 in. frame with 7/16 in. SentryGlas laminated glass; +90/-90 psf with 7/16 in. PVB laminated.
• Eurocraft EC-100 fixed window: up to ±120 psf with 7/16" PVB and up to ±180 psf with 9/16" SentryGlas on smaller units (ECI022 glass tables).

SentryGlas does not always rate higher.

The interlayer is one part of a tested system. On the Mr. Glass MG-3000 outswing door, drawing 18-36F rates PVB glass at ±80 psf on smaller sizes and SentryGlas at +65/−70. Composite PVB interlayers also exist. Saflex Storm, for example, bonds PVB to a PET (polyester) film for tear resistance, performs in both large- and small-missile applications and filters more than 99% of UV rays. Only the approval drawing for the exact product tells you which glass build earns which rating.

When PVB is perfectly adequate.

For many homes, PVB is the right choice. If the design pressure your opening needs is within the PVB rating on the approval drawing, a PVB laminate passes the same large-missile impact and cyclic pressure tests as any other approved glass in that window. Typical single-family openings with moderate pressures, budget-minded projects and windows with no exposed glass edges are all good fits. The Mr. Glass MG-350 SH single-hung, for example, uses one 5/16 in. laminated glass build and is rated +65/−80 psf. PVB laminates also block UV, cut outside noise and hold broken glass in place.

When SentryGlas is worth the upgrade.

Choose SentryGlas when the opening needs a design pressure the PVB glass cannot reach, which is common on tall or wide units, coastal and high-exposure sites, corner zones and upper floors. It also makes sense for very large fixed glass, for the clearest long-term look, and for buyers who value a longer glass warranty. Eurocraft's limited warranty covers SentryGlas laminated glass for 10 years and PVB laminated and insulating glass for 5 years. A SentryGlas interlayer adds noticeably to cost because it is a specialty structural material, so specify it where the rating or size calls for it.

The bottom line.

SentryGlas is stiffer, clearer and more stable at the edges, and it usually unlocks higher design pressures and larger sizes. PVB is proven, lower in cost and fully approved where its ratings cover your openings. Neither is better in every case. What governs is the approval for the exact product, size and glass build, together with the pressure your opening requires. True Impact confirms that approval for each opening before we quote or permit it.