Retroreflective Sheetings Used for Sign Faces
Important Note: The current state of the retroreflective sheeting market is continuing to change, due to development of new sheetings, requested changes to ASTM D4956, and changes in product offerings by manufacturers. This webpage will try to keep up with current events in reflective sheetings as they develop.
There are a number of different types of retroreflective sheetings in use on highway signs.
Some types, as classified by ASTM D4956, are:
- Type I, also known as Engineer Grade:
Basic reflective sheeting, made up of either very small glass beads enclosed in a translucent pigmented substrate or a dual-layer prismatic sheeting with moderate retroreflectivity. Has no distinctive identifying pattern, other than, of course, it reflects. This material is one of the most durable (in its ability to withstand rough handling) of all the sign sheeting products. Generally regarded to have a seven year service life. Rendered functionally obsolete for most sign use by 2009 MUTCD requirements for minimum retroreflectivity levels, but still used for highway advertising, vehicle graphics, and utility-grade reflectivity.
- Type II, also known as Super Engineer Grade:
Similar to Type I, except it uses larger glass beads, providing about twice the level of reflectivity of Type I sheeting. This sheeting can be identified by small trademarks which are screened into the sheeting (varying by manufacturer). Generally regarded to have a ten year service life. Also used for vehicle graphics.
- Type III, also known as High Intensity:
This sheeting is know as an "encapsulated lens" sheeting, made of 2 layers - an outer translucent pigmented layer, and an inner reflective layer faced with glass beads. The two layers are connected by a lattice, hence its distinctive 'honeycomb' appearance, where the lattice pattern varies by manufacturer for easy identification. Generally regarded to have a ten year service life. Rendered functionally obsolete by lower-cost alternatives such as Type IV.
- Type IV:
This is also a multi-layer sheeting, except that the reflective layer is made of microscopic cube-corner reflectors instead of glass beads - known as a "microprismatic" layer. This sheeting can be distinguished by a pattern of small squares or bars superimposed upon the lattice grid. Generally regarded to have a ten year service life.
- Type V:
This sheeting is made of a metallized microprismatic material. Used in delineators, raised pavement markers, and other applications requiring flexibility and durability. Generally regarded to have a five year service life.
- Type VI:
A vinyl backed microprismatic material. This sheeting differs from all other types by being composed of a flexible vinyl cloth, allowing it to be used for clothing and roll-up signs. Generally regarded to have a two year service life, depending on handling and use.
- Type VII:
This is also a microprismatic sheeting. This can be distinguished by the diamond-shaped lattice separating the sheeting layers, and a "coarse" grain to the microprisms. This sheeting provides high retroreflectivity levels at shallow viewing angles. Cost is about 5 times that of Type I. Generally regarded to have a ten year service life.
- Type VIII:
Also a microprismatic sheeting similar in design to Type VII and IX, but with distinguishing characteristics similar to Type IV. Generally regarded to have a ten year service life.
- Type IX:
A microprismatic sheeting very similar to Type VII, distinguished from Type VII by the "fine" grain of the microprisms. This sheeting provides relatively high retroreflectivity levels at a wider range of viewing angles. Generally regarded to have a ten year service life.
- Type X:
A microprismatic sheeting very similar to Types VII-IX, and has similar performance characteristics. Generally regarded to have a ten year service life.
- Type XI:
A microprismatic sheeting very similar to Types VII-IX, but providing high retroreflectivity at both shallow and wide angles. Generally regarded to have a ten to twelve year service life.
Important Note: The Types used in the ASTM sheeting specifications do not necessarily imply relative performance; i.e. a "higher"-type sheeting isn't necessarily better than a "lower"-type sheeting - it just meets different performance characteristics. Also note that some sheetings can meet the criteria of several ASTM Types.
Nearly all sheetings are available with pressure-sensitive backings for attachment to sign surfaces. Some sheetings are available with heat-activated backings, but with changes in sign manufacturing technology this type of adhesive is becoming less popular and less available.
Sign legends for retroreflective signs are produced by the following methods:
- Cut-out Letters and Symbols: directly applied to the sign face.
- Demountable Copy: This legend is made of reflective sheeting applied to thin aluminum, which is then cut out into the letter and legend shapes and then riveted to the sign face. This permits the sign legend to be changed or removed without having to replace or cover the sign panel.
- Positive Silk-screen: Used for signs with legends darker than the background, such as most regulatory and warning signs. The legend is applied directly onto the colored sign face with opaque ink.
- Negative Silk-Screen: Used for signs with legends lighter than the background, such as STOP signs or Interstate shields. The process begins with a white sign face, then a translucent ink is applied onto the sign face, with the exception of the legend (or regions of other colors. This produces a white legend on a colored background.
- Overlay Film: Also used for signs with legends lighter than the background. The process begins with a white sign face, then the overlay film in the appropriate color is cut to remove the sections where the white is to show through. This overlay film is then applied onto the sign face.
Colored inks used in sign silk-screening are translucent to allow reflectivity through the ink, whereas black ink used for signs is opaque.
Sheeting types normally fail in different ways, depending on how they are structured.
Single-layer types, such as Type I or II, usually fail by gradually losing their retroreflective intensity. This is due to increasing opacity of the pigmented material caused by ultraviolet ray exposure due to sunlight.
Multi-layer sheetings, such as Type III through Type XI, often fail structurally - the outer colored layer delaminates and falls off, exposing the underlying reflective layer to the elements, and ruining the contrast needed for legibility.
If properly applied and sealed to a good surface, most reflective sheetings are quite water, ice, and salt resistant.
Special thanks to Seth Chalmers of Chalmers Engineering Company and H. Gene Hawkins Jr. of Texas A&M University for their invaluable assistance in gathering this information.
More information may also be found at the Federal Highway Administration's webpages on sign retroreflectivity.
FHWA Retroreflective Sheeting Identification Guide
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Updated 09 December 2015
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Retroreflective Sheeting Identification Guide provided courtesy of Federal Highway Administration.
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