Polyurethane Tubing

Why polyurethane is a go-to material for medical tubing

Polyurethane tubing, often called urethane tubing, is one of the most widely used materials in catheter and medical tubing design. Polyurethane (PUR) was invented in 1937. Polyurethanes are segmented polymers: each chain has a soft segment that provides flexibility and a hard segment that provides strength. By changing the ratio between the two, resin makers produce grades that range from soft and rubbery to stiff and rigid, which is why one material family can cover so many device requirements.

Compared with nylons, polyurethanes are more flexible and bond well to almost any surface, which simplifies device assembly. Polyurethane tubing can be transparent or opaque. The main drawback to plan for is tackiness, which can matter in applications where tubes slide against each other or through a sheath.

Polyurethane properties at a glance

The physical and mechanical properties of any polyurethane depend on its chemistry, structure, chain length and the bonds between chains. The ranges below span the soft to rigid grades we extrude. Datasheets for each trade name are linked further down the page.

Medical-grade polyurethanes may be suitable for remaining in the body for as long as 30 days, and depending on grade they can be sterilized with dry heat, ethylene oxide (EtO) or gamma radiation.

Values are typical resin supplier data for reference only. Confirm final material selection and biocompatibility against your own device requirements and supplier documentation.

Where polyurethane tubing is used

Melt-processable polyurethanes are often used to make catheters, especially multi-lumen catheters, and for short-term implants. Their properties make them suitable for nearly every extrusion type we run:

• Bump tubing that tapers from a larger proximal end to a smaller distal end
• Co-extrusions, multi-layered walls and striped tubing
• Micro-extrusions for minimally invasive and pediatric devices
• Single-lumen and multi-lumen tubing
• Profile extrusions with non-round shapes or lumens

Aliphatic vs. aromatic polyurethanes

Medical polyurethanes fall into two chemical families. Aliphatic polyurethanes, such as Tecoflex® and some Carbothane® grades, have carbon atoms linked in open chains. They do not yellow over time, which matters for clear tubing. Aromatic polyurethanes, such as Tecothane® and Texin®, have carbon atoms linked in a ring structure, which gives them enhanced chemical stability and good chemical resistance. Carbothane is also polycarbonate-based, giving it a higher relative degree of biostability than Tecoflex.

What we watch when extruding polyurethane

Polyurethane is forgiving in a finished device but demanding on the extrusion line. Lot-to-lot variability in raw material is a real challenge, especially with polyurethanes. Multi-lumen extrusion is very sensitive to changes in viscosity and melt flow index (MFI). Tools that make a perfect tube from a lot with an MFI of 9 may not work at all with a lot of the same material at an MFI of 3. When we validate a part, we define and specify the acceptable MFI range that works.

Polyurethane is also one of the materials we use for our thinnest walls. We consistently extrude polyurethane tubing with walls as thin as 12.5 microns (0.0005 inch), along with Pebax, FEP and PEEK.

Durometer matters too. When a softer distal section must match the geometry of a stiffer proximal section, the tools that produced one end may not produce the other, because the two durometers flow differently. Our in-house tooling shop designs for that from the start instead of discovering it during validation.