PEEK vs PI (Polyimide) vs PTFE: Which High-Temp Tube for Your Job?

Three polymers, three very different failure modes. Get the call wrong and you do not get a cheaper tube - you get a field failure at the worst possible moment.

The question that settles most of the room

Before you reach for a data sheet, ask one thing: does this tube have to carry load, or just contain a fluid? That single question decides this whole comparison.

• PTFE - a chemical barrier. Cheap, -200 C to +260 C, inert to almost everything. But it cold-flows under load and has no structural stiffness.
• PI (polyimide) - the radiation and temperature king. -269 C to +400 C continuous, survives environments that kill everything else. Expensive, hard to machine.
• PEEK - the structural workhorse. 260 C continuous with real tensile strength and wear resistance, at a price that still hurts but buys mechanical duty.

The tolerance wall that actually bites

In thin-wall tubing the material comparison is the easy part. The painful part is what the catalogue does not print: concentricity and wall uniformity. A 0.5 mm wall PI tube that is 0.48 mm on one side and 0.53 mm on the other passes a nominal spec but fails a 200 C thermal-cycle test because the thin side ages first. For semiconductor and sensor leads where ID/OD tolerance and a clean, particle-free bore matter, the grade and the die matter more than the polymer name. See the polyimide radiation and semiconductor note.

Property	PTFE	PI (polyimide)	PEEK
Continuous temp	-200 to +260 C	-269 to +400 C	up to +260 C
Radiation resistance	Poor	Excellent	Good
Tensile strength	~25 MPa	~70 MPa	~100 MPa
Thin-wall ID/OD tolerance	+/-0.03 to 0.05 mm	+/-0.02 to 0.05 mm	+/-0.03 to 0.05 mm
Relative cost	1x	3-5x	3-5x
Typical use	Chemical barrier	Sensors, aerospace, radiation	Loaded, wearing parts

The honest engineering rule

Data density point: in real projects over the last few years, PTFE wins every "just seal it" application, PEEK wins every "it must not flex or wear" application, and PI wins every radiation or extreme-temperature question that nothing else survives. Budget is usually the tie-breaker, not performance. For thin-wall PI, the tie-breaker is whether the supplier can hold the bore - not the price.

"PTFE is a barrier, PEEK is a structure, polyimide is a survivor. You are not choosing polymers - you are choosing failure modes, and then choosing who can hold the tolerance."

Specify the tube for a sensor or semiconductor line and polyimide is the premium answer. For loaded tubing at 260 C, look at PEEK where dimensional stability matters.

Bottom line: tell us the temperature, whether radiation is present, whether the tube carries load, and the ID/OD tolerance you must hold. We will name the grade and send you a drawing-ready spec - no upselling.