The reason Plexiglass acrylic plastic is widely used in so many applications is because it
has a better combination of properties for certain types of jobs than other
materials such as metals, woods, and glass. It also has properties which must
be considered in design and installation. All materials have limitations -
metals rust, woods warp, and glass breaks - yet each is a basic material in
industry because these limitations are taken into account in product design,
installation and use. Similarly, the characteristics of acrylic sheet must be
understood for the most effective use of the material. Taking into account
these factors in design, fabrication and installation will insure success in
the finished product or part.
Stress Limits - Plexiglass Acrylic sheet offers good tensile, impact, and flexural
strength properties as shown in the table below; however, stress considerably
below the test values shown will produce light surface checking or fractures
known as crazing. To avoid crazing, loads should not exceed 1,500 psi.
Tensile Strength 10,500 psi (Tensile strength is a measure of the force
required to pull a specimen apart.)
Flexural Strength 16,000 psi (Flexural strength is a measure of the force
required to break a specimen by bending it.)
Compressive Strength 18,000 psi (Compressive strength is a measure of the
compressive load required to cause failure.)
Modulus of Elasticity 450,000 psi (Modulus of elasticity is a measure of the
force required to produce a given change in dimension. A high modulus is
associated with rigidity and a material's ability to hold its shape under
Thermal Expansion and Contraction - All materials expand and contract to a
greater or lesser degree due to changes in temperature and humidity. Allowances
must be made for these changes in the construction and fabrication of products;
for example, the expansion joints in cement sidewalks and on steel bridges.
Plexiglass Acrylic sheet is subject to greater dimensional change, due to thermal
expansion and contraction, than other materials with which it is used in
Comparison of Co-Efficient of Thermal Expansion
Plexiglass Acrylic Sheet vs. Other Materials
Acrylic Sheet .0000410
Plate Glass .0000050
For indoor applications where temperature normally remain the same (+/- 20
degrees F), acrylic sheet does not generally require special considerations for
expansion and contraction other than providing for a snug rather than tight fit
since its movement is approximately 1/32 of an inch per foot length for each 20
degrees of temperature change. In outdoor use where temperature varies widely,
acrylic sheet should be handled in accordance with the following
1. Sheets or panels should be installed in a channel frame engaging the edges
of the material so that it is free to expand and contract without restraint.
2. The channel frame depth should be sufficient to allow for thermal
contraction of the sheet without withdrawal of the edges of the frame.
3. Through-bolting or other inflexible fastenings which do not provide for
expansion and contraction may cause failure of the installation.
4. Before installation in the channel frame, the sheet or panel should be cut
sufficiently shorter than the channel frame dimensions to allow for thermal
5. Sealant compounds and tapes should be types which are sufficiently
extensible to accommodate thermal expansion and contraction of the material and
which adhere to both sheet and frame. A practical rule to follow in outdoor
installations is that the frame depth should be 1/4" plus 1/8" per running foot
of acrylic sheet in length and width to provide for contraction. To provide
expansion clearance, the flat sheet should be cut 1/16" per running foot
shorter than the frame depth in both dimensions.
Rigidity - Plexiglass Acrylic sheet is not as rigid as many other materials such as metal,
wood, and glass. This can cause the material to deflect under load and
foreshorten as a result of the deflection. Observation of the following
recommendations will contribute to the good performance of the finished part.
1. Channels engaging the edges of the sheet must be sufficiently deep to allow
for foreshortening of the sheet due to deflection under load, as well as
thermal expansion and contraction.
2. Thermoforming the Plexiglass sheet into dome-shaped or corrugated sheets increases its
rigidity. Wherever practical, formed panels should be used in large unsupported
area usage, where wind loads or snow loads are involved.
3. If it is not practical to form the sheet, increasing the thickness of a flat
sheet will impart greater rigidity to the panel.
4. Another possibility is to insert a curved wedge under a Plexiglas skylight
to give it a convex shape.
5. As a general rule, any horizontal outdoor glazing for skylights, etc.,
should be 1/4" thickness for minimum deflection with maximum unsupported span
Notch Sensitivity - Like glass and many other materials, Plexiglass acrylic plastic is
notch sensitive. Notches and chipping along the edges of the sheet, at drilled
holes, and inside corner cuts are potential points of cracking or breaking.
Scraping, sanding or joining the rough cut edges will eliminate these notches
and insure the maximum impact resistance of the part. Inside corner cuts should
be avoided whenever possible or at least be designed to have a slight radius.
Surface Hardness - The surface hardness of acrylic sheet is approximately equal
to that of copper or brass. Abrasives will scratch the surface of acrylic. This
is not ordinarily a handicap in the use of colored or patterned sheet but may
be one in the use of clear sheet where scratch-free appearance is desired. The
exercise of reasonable care in cleaning colorless acrylic sheet will minimize
Combustibility - Acrylic plastic must be used with an appreciation for the fact
that it is a combustible material. The fire precautions observed to protect
wood and other ordinary combustibles should be used to protect acrylic plastic
from ignition sources and involvement in fire. Applications subjected to high
heat sources of flame such as high wattage incandescent light bulbs, radiators,
heaters, fire places or candles, etc. should be avoided. Items normally made
from non-combustible materials should be considered carefully before making
them in acrylic as an unknowing user might assume they are safe when they
might, in fact, present a hazard.
Service Temperature - The maximum temperature at which acrylic plastic can be
subjected to for any period of time is 180 degrees F to 200 degrees F. The
material softens when heated to temperatures above 260 degrees F which is 40
degrees below the temperature used in thermoforming, and 300 degrees below its
ignition temperature. Applications subjected to high heat sources should be
avoided or temperatures checked to allow for an adequate safety factor. An
alternative clear plastic to use would be Tuffak Polycarbonate with a service
temperature of 270 degrees F.