Asphalt shingles are made of fiberglass mat, asphalt coating, and ceramic granules. Learn the science behind each layer and how it protects your home.
Most homeowners know that their roof is covered in asphalt shingles. Far fewer know what an asphalt shingle is actually made of — and that gap in understanding makes it harder to evaluate product quality, compare warranties intelligently, or recognize why a shingle is failing prematurely.
Asphalt shingles are more sophisticated than they appear. A modern fiberglass asphalt shingle is a precisely engineered composite of four distinct components, each serving specific functions. Understanding those components is the foundation of understanding roofing quality. For context on how asphalt shingles compare to other roofing materials, see our complete guide to types of roofing materials.
A standard asphalt shingle is built in layers, each bonded to the one above and below. From bottom to top, the components are:
Each of these components varies in quality between manufacturers and between product lines within the same manufacturer. Knowing what each does explains why higher-quality shingles cost more and last longer.
The fiberglass mat is the structural backbone of a modern asphalt shingle. It is a non-woven sheet of glass fibers — the same basic material as fiberglass insulation, but formed into a flat, paper-like sheet rather than fluffy batts. Glass fibers are randomly oriented and bonded together with a thermosetting resin binder, creating a mat that has consistent strength in all directions.
The fiberglass mat provides tensile strength — resistance to tearing and stretching. Without a strong mat, the asphalt layers above and below would deform and crack under mechanical stress from foot traffic, thermal expansion, and wind loading. The mat also provides dimensional stability: it resists the tendency of asphalt to flow or deform under sustained heat exposure.
The mat is the reason modern shingles are called "fiberglass shingles" in the industry, even though the exterior appearance is identical to the older organic mat products.
Mat quality is one of the most important variables in shingle durability, and it is also one of the least visible. Higher-quality fiberglass mats have greater fiber density, more consistent binder distribution, and higher tensile strength ratings. They are more resistant to tearing during installation, provide better support for thicker asphalt coatings, and resist the fatigue cracking that eventually develops in lower-quality mats after years of thermal cycling.
Before fiberglass mats became standard in the 1980s, asphalt shingles were built on organic cellulose mats made from recycled paper, rags, and wood fiber. Organic-mat shingles absorbed more asphalt (making them heavier and more flexible in cold weather) but were significantly more vulnerable to moisture, dimensional distortion, and fire. Modern fiberglass-mat shingles are lighter, more fire-resistant, and more dimensionally stable. They are now the universal standard. Organic-mat shingles are no longer manufactured.
After the fiberglass mat is produced, it is fed through a bath of liquid asphalt that thoroughly saturates the mat — filling all the microscopic gaps between fibers and bonding fully to both surfaces. This saturant is a refined petroleum product: crude oil is processed to remove lighter fractions (which become gasoline, diesel, and other fuels), leaving behind the heavy, viscous residue that becomes roofing asphalt.
The saturant's primary function is waterproofing at the mat level. The glass fibers themselves are not waterproof — the asphalt filling every gap in the mat is what prevents water from passing through. The saturant also provides the first layer of flexibility, allowing the shingle to bend rather than crack as it is handled during installation.
Asphalt quality varies in several ways. The most important quality variable for a roofing consumer is the softening point — the temperature at which the asphalt begins to soften and flow. Asphalt with a higher softening point is more resistant to high-temperature deformation, which matters enormously in Tennessee where roof surface temperatures can exceed 150 degrees Fahrenheit during summer. Low-quality asphalt with a low softening point can develop thermal creep — slow downward movement of the asphalt layer — on steep pitches in sustained heat.
After saturation, a second, harder asphalt compound is applied to both surfaces of the saturated mat. This top coat is typically stiffer and more weather-resistant than the saturant, formulated specifically for surface exposure. The top coat is where granules are embedded on the exposed upper surface, and where a release coating is applied to the bottom surface to prevent shingles from sticking together in the bundle.
Premium shingle products use polymer-modified asphalt formulations rather than straight refined asphalt. Styrene-Butadiene-Styrene (SBS) and Atactic Polypropylene (APP) are the most common polymer modifiers added to roofing asphalt. These additives extend the asphalt's usable temperature range in both directions: lower temperatures remain flexible (reducing cold-weather cracking) and higher temperatures resist softening (reducing thermal deformation). In Tennessee's climate, where a roof must perform from 15-degree winter nights to 155-degree summer surface temperatures, polymer-modified asphalt delivers measurably better longevity.
The granule layer is the most visible component of an asphalt shingle and the one that most directly determines its surface performance. Granules are also the component whose degradation is most visible to homeowners over time — the slow loss of granules is one of the primary indicators of shingle aging.
Roofing granules are small, angular mineral particles — typically crushed rock (slate, basalt, or quartzite) — that are coated with ceramic pigments and then kiln-fired to permanently fuse the color into the particle. The base rock provides hardness and weather resistance. The ceramic coating provides color stability — the ability to maintain color integrity under prolonged UV exposure without fading.
The granule layer's most critical function is UV protection. Asphalt degrades rapidly when exposed directly to ultraviolet radiation — it becomes brittle, cracks, and eventually crumbles. The granule layer creates a UV-blocking surface that shields the asphalt layers below from direct sun exposure. As long as granules remain in place and adequately cover the asphalt surface, the shingle is protected. When granules are lost — through weathering, storm impact, or manufacturing defects — the exposed asphalt degrades rapidly.
This is why granule loss is such a meaningful early warning sign of shingle end-of-life. It is not the granule loss itself that causes failure — it is the accelerated asphalt degradation that follows when the granule protection layer is compromised.
Once an asphalt shingle starts losing granules, the process accelerates. Exposed asphalt bakes in the sun, becomes brittle, cracks, and releases more granules from the surrounding area. What starts as isolated granule loss from minor storm damage or normal weathering can spread rapidly once the protective layer is compromised. If you notice significant granule accumulation in your gutters after rain, get a professional inspection — this is a meaningful indicator of where your shingle's remaining life stands.
Ceramic-coated granules are inherently fire-resistant. When installed as a complete roof system over solid decking with a compliant underlayment, asphalt shingles with a full granule layer achieve a Class A fire rating — the highest possible designation. The granule layer's thermal mass absorbs radiant heat from an external fire source before it can reach the asphalt layers below. As granule coverage is lost, the fire resistance advantage is reduced.
The ceramic coating on roofing granules is responsible for the shingle's color. High-quality granule coatings maintain color integrity for decades under UV exposure. Lower-quality coatings fade, giving the roof a washed-out, aged appearance well before the shingle's structural life is exhausted.
Premium laminate shingle products use "blended granule" technology: a mixture of granules in several distinct colors are blended and applied together to create a variegated, multi-tonal appearance. A simple charcoal shingle from a premium manufacturer might blend five or more shades of gray with occasional warm or cool accent granules, creating a surface that looks like natural slate from the street. A budget product uses simpler, two-color blends that look flat by comparison.
Some manufacturers incorporate copper or zinc particles into their granule blends to inhibit the growth of Gloeocapsa magma, the algae responsible for the dark black streaks common on older roofs in humid climates like Tennessee's. The trace metals leach slowly from the granule surface when moistened by rain, creating a roof environment that is hostile to algae colonization. Products from GAF (StainGuard), Owens Corning (TruDefinition with algae protection), Atlas (Scotchgard Protector), and CertainTeed (StreakFighter) all incorporate this technology. For Tennessee homeowners, algae-resistant granules are worth the modest premium they carry.
On the back of each shingle, near the bottom edge, is a strip of thermoplastic adhesive — often called the "sealant strip" or "self-sealing strip." This strip is inactive at room temperature but softens and becomes permanently adhesive when warmed by sunlight after the shingle is installed.
The adhesive strip bonds each shingle course to the shingle course below it. This bond is the most important wind resistance mechanism in an installed shingle roof — not the nails alone. The nails hold the shingle down at the nailing zone; the adhesive strip holds the free (exposed) edge of the shingle down in wind events. A properly activated adhesive strip dramatically reduces the tendency of shingle edges to lift under wind pressure.
The significance of this becomes apparent in storm events: shingles that have not fully sealed (due to cold installation temperatures, shading, or manufacturing defects) are far more vulnerable to wind uplift than properly sealed shingles. Contractors installing in cold weather should apply roofing cement to ensure adhesion that the self-sealing strip cannot achieve without solar warming.
Understanding what shingles are made of makes it easier to understand how and why they fail over time. The aging process follows a predictable sequence.
Early years (0–5 years): Granules may lose some initial loose particles as the shingle settles. Minor granule accumulation in gutters is normal during this period. The shingle is in its prime performance window.
Middle years (5–15 years): Normal UV-driven asphalt oxidation begins, slightly reducing flexibility. Granule adhesion remains strong in quality products. The self-sealing strip maintains adhesion. Some color fading may be visible in lower-quality products.
Later years (15–25 years): Accelerating granule loss as the asphalt binder softens and contracts with thermal cycling, releasing granule adhesion. Exposed asphalt becomes brittle. Edges and corners may begin to curl or cup. Valley areas and south-facing slopes (highest UV exposure) show earliest failure.
End of life (20–30+ years): Significant granule loss across the roof surface. Brittle, cracking asphalt. Compromised adhesive strip adhesion from thermal degradation. Flashing sealants have typically failed. The roof is no longer performing its waterproofing function reliably and replacement is needed.
When comparing shingle products, the composition details — though rarely prominently marketed — are the most reliable quality indicators:
For a comparison of how the leading manufacturers perform on these quality factors, see our best roofing shingle brands guide. For information on the different types of shingle products built from these materials, see our types of asphalt shingles guide.
Our shingle roofing services page explains how Opus Roofing selects materials and approaches shingle installations for Tennessee homes.
Our team can walk you through shingle options, explain the quality differences between product lines, and give you an honest recommendation for your home.
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