A Guide to Plastics Commonly Used in Blow Molding

Choosing the right plastic resin for your blow molding project can be a challenge. Cost, density, flexibility, strength, and more all factor into what resin is best for your part.

Here’s an introduction to the characteristics, benefits, and drawbacks to resins commonly used in blow molding.

High Density Polyethylene (HDPE)

HDPE is the world’s #1 plastic and the most commonly blow molded plastic material. It’s used in a vast array of products, including bottles for consumer liquids such as shampoo and motor oil, coolers, play structures, fuel tanks, industrial drums, and carrying cases. It’s molder-friendly, translucent and easily colored, and chemically inert (FDA approved and perhaps the safest of all plastics). PE the most commonly recycled resin with recycling code designation 2.

Comparative value generalizations

Cost$0.70/lb.Density0.95 g/cc
Low Temp-75°FHigh Heat Deflection160°F
Flex Modulus1,170 mpaHardnessShore 65D

Low Density Polyethylene (LDPE)

Variations of LDPE include linear-low (LLDPE) and combinations with ethyl-vinyl-acetate (LDPE-EVA). LDPE is used for softer products that require a high level of stress crack resistance or flexibility. Generally, the higher the ethyl-vinyl-acetate (EVA) content, the softer the molded part. Common applications include squeeze bottles, traffic channelizers, and boat fenders. The highest usage is blown film for plastic bags. It is also molder-friendly, translucent and easily colored, chemically inert, and commonly recycled under code 4.

Comparative value generalizations

Cost$0.85/lb.Density0.92 g/cc
Low Temp-80°FHigh Heat Deflection140°F
Flex Modulus275 mpaHardness Shore 55D

Polypropylene (PP)

PP is the world’s #2 plastic — it’s an extremely popular injection molding resin. PP is similar to HDPE, but slightly stiffer and lower density, which provides some advantages. PP is commonly used in elevated temperature applications, such as dishwasher tubes and medical parts that require autoclave sterilization. It’s molder-friendly as well as translucent and easily colored. Some clarified versions provide “contact clarity.” PP recycling is common under code 5.

Comparative value generalizations

Cost$0.75/lb.Density0.90 g/cc
Low Temp0°FHigh Heat Deflection170°F
Flex Modulus1,030 mpaHardness Shore 75D

Polyvinyl Chloride (PVC)

Although PVC is the world’s #3 plastic, it has been heavily scrutinized for using cadmium and lead as stabilizers, releasing hydrochloric (HCl) acids during processing, and releasing residual vinyl chloride monomers after molding (most of these problems have been reduced). PVC is translucent and comes in rigid and soft forms — the soft resin is typically used in blow molding. Common applications include soft medical parts, bellows, and traffic cones. Special processing equipment is recommended to prevent corrosion from HCl. PVC is recyclable under code 3.

Comparative value generalizations

Cost$1.15/lb.Density1.30 g/cc
Low Temp-20°FHigh Heat Deflection175°F
Flex Modulus2,300 mpaHardness Shore 50D

Polyethylene Terephthalate (PET)

PET is a polyester that is usually injection blow molded into clear containers. While it isn’t impossible to extrusion blow mold PET, it is less common, as the resin requires extensive drying. The largest PET blow molding market is for soft drink and water bottles. PET recycling rates are growing under recycle code 1.

Comparative value generalizations

Cost$0.85/lb.Density1.30 g/cc
Low Temp-40°FHigh Heat Deflection160°F
Flex Modulus3,400 mpaHardness Shore 80D

Thermoplastic Elastomers (TPE)

TPEs are used to replace natural rubber in molded parts. The material is opaque and can be colored (typically black). TPEs are commonly used in automotive suspension covers and air intake ducts, bellows, and grip surfaces. It molds well after drying and generally reprocesses well. However, recycling rates are somewhat limited under code 7 (other plastics).

Comparative value generalizations

Cost$2.25/lb.Density0.95 g/cc
Low Temp-18°FHigh Heat Deflection185°F
Flex Modulus2,400 mpaHardnessShore 50D

Acrylonitrile Butadiene Styrene (ABS)

ABS is a relatively hard plastic, used to injection mold football helmets. Blow molding grade ABS is typically opaque and colored for use in electronics housings and small appliances. ABS molds well after drying. However, parts made from ABS aren’t as chemically resistant as PE or PP, so caution must be used with parts that come in contact with chemicals. Various grades can pass the Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances Testing (UL 94), Classification V-0. ABS is recyclable as code 7, but its toughness makes grinding difficult.

Comparative value generalizations

Cost$1.55/lb.Density1.20 g/cc
Low Temp-40°FHigh Heat Deflection190°F
Flex Modulus2,680 mpaHardnessShore 85D

Polyphenylene Oxide (PPO)

PPO is an opaque resin. It requires drying and has a limited drawdown capacity during molding. This restricts designers to PPO parts with generous blow ratios or flat shapes, such as panels and desktops. Molded parts are stiff and relatively strong. Like ABS, PPO grades can pass UL 94 V-0 flammability criteria. It can be reprocessed, and a few recyclers accept it under code 7.

Comparative value generalizations

Cost$3.50/lb.Density1.10 g/cc
Low Temp-40°FHigh Heat Deflection250°F
Flex Modulus2,550 mpaHardness Shore 83D

Nylon/Polyamides (PA)

Nylon melts quickly, so it’s more commonly used in injection molding. The resins used for extrusion blow molding are typically variants of nylon 6, nylon 4-6, nylon 6-6, and nylon 11.

Nylon is a reasonably priced translucent material that has decent chemical resistance and performs well in high heat environments. It’s often used to make tubes and reservoirs in automotive engine compartments. One special grade, nylon 46, withstands continuous temperatures up to 446°F. Some grades meet UL 94 V-2 flammability criteria. Nylon can be reprocessed, in certain circumstances, under recycled code 7.

Comparative value generalizations

Cost$3.20/lb.Density1.13 g/cc
Low Temp-40°FHigh Heat Deflection336°F
Flex Modulus2,900 mpaHardness Shore 77D

Polycarbonate (PC)

The toughness of this clear, workhorse material makes it perfect for products ranging from eyeglasses to bullet-proof glass in jet cockpits. It’s also commonly used to make 5-gallon water bottles. PC must be dried before processing. It molds well in basic shapes, but requires serious evaluation for complex shapes. It’s also very difficult to grind, but does reprocess under recycle code 7.

Comparative value generalizations

Cost$2.00/lb.Density1.20 g/cc
Low Temp-40°FHigh Heat Deflection290°F
Flex Modulus2,350 mpaHardness Shore 82D

Polyester & Co-polyester

Polyester is often used in fiber. Unlike PET, modified polyesters like PETG (G = glycol) and co-polyester are clarified materials that can be extrusion blow molded. Co-polyester is sometimes used as a substitute for polycarbonate (PC) in container products. It’s similar to PC, but it’s not quite as clear or as tough and it doesn’t contain bisphenol A (BPA), a substance that raises health concerns in some studies. Co-polyesters show some cosmetic degradation after reprocessing, so recycled materials have somewhat limited markets under code 7.

Comparative value generalizations

Cost$2.50/lb.Density1.20 g/cc
Low Temp-40°FHigh Heat Deflection160°F
Flex Modulus2,350 mpaHardness Shore 82D

Urethane & Polyurethane

Urethanes provide performance properties that are popular in coatings like paint. Urethanes are generally more elastic than polyurethanes, which have to be specially formulated to become thermoplastic urethanes. The thermoplastic grades can be cast and extrusion or injection blow molded. The material is most often used as one layer in multi-layer blow molding. Ionomer versions can be used to impart gloss. Recycling is generally limited to in-house reprocessing under the code 7.

Comparative value generalizations

Cost$2.70/lb.Density0.95 g/cc
Low Temp-50°FHigh Heat Deflection150°F
Flex Modulus380 mpaHardness Shore 60A – 80D

Acrylic & Polystyrene

The clarity of these relatively low-cost resins leads customers to request them for applications such as lighting lenses. The material is normally vented during extrusion and tends to melt into a liquid state, which makes the success rate in extrusion blow molding relatively low. Producers and compounders continue to work on processing improvements for extrusion grades with some success. The material can be recycled, usually for use in injection molding, under code 6.

Comparative value generalizations

Cost$1.10/lb.Density1.00 g/cc
Low Temp-30°FHigh Heat Deflection200°F
Flex Modulus2,206 mpaHardness Shore 85D

New Materials

Producers and compounders provide an amazing array of enhanced resin properties. More are introduced every day that have a wide variety of properties. For example, TPC-ET, a thermoplastic elastomer of co-polyester, is replacing traditional TPEs in elevated temperature conditions. New TPU thermoplastic urethane elastomers resists oils, wear, and tear better than traditional TPE. You need a supplier who tracks developments throughout the plastics industry.

Comparative value generalizations by plastic type

Cost

Density

Low TempHigh Temp Flex ModulusShore

Hardness

Recycle Code
HDPE$0.70/lb0.95 g/cc-75°F160°F1,170 mpa65D2
LDPE$0.85/lb0.92 g/cc-80°F140°F275 mpa55D4
PP$0.75/lb0.90 g/cc0°F170°F1,030 mpa75D5
PVC$1.15/lb1.30 g/cc-20°F175°F2,300 mpa50D3
PET$0.85/lb1.30 g/cc-40°F160°F3,400 mpa80D1
TPE$2.25/lb0.95 g/cc-18°F185°F2400 mpa50D 7
ABS$1.55/lb1.20 g/cc-40°F190°F2,680 mpa85D7
PPO$3.50/lb1.10 g/cc-40°F250°F2,550 mpa83D7
PA$3.20/lb1.13 g/cc-40°F336°F2,900 mpa77D7
PC$2.00/lb1.20 g/cc-40°F290°F2,350 mpa82D7
Polyester & Co-polyester$2.50/lb1.20 g/cc-40°F160°F2,350 mpa82D7
Urethane Polyurethane$2.70/lb0.95 g/cc-50°F150°F380 mpa60A-80D7
Acrylic -Styrene $1.10/lb1.00 g/cc-30°F200°F2,206 mpa85D6

The possibilities for innovation in materials are endless. Custom-Pak will always strive to stay abreast of the latest developments and provide the best advice for selecting materials to make your project a success.

We hope this general information on plastic materials is helpful. Please Note: Specific grades of these materials will have properties much different than presented here. We highly recommend that you get a material properties data sheet specific to the resin you are researching so you verify the exact test value for every property.

Plastic materials are sold in a dynamic market. Prices change frequently for many reasons. The price generalizations provided are not intended to be used for product quotations.

Looking for more information on materials choices? Check out our blog on blow molding plastics and sustainability or finding current resin prices.

Thank you.