Mylar Insulating Sleeve
Product Description
Product Detail
What Mylar Is and Why the Industry Specifies It
Mylar is the industry-recognised bolt and sleeve insulating material for flange insulation kits. It is a biaxially oriented polyester (PET) film with high tensile strength, high dielectric strength and near-zero water absorption — the three properties that matter most for a bolt-hole sleeve.
In a bolted flanged joint, the sleeve has to survive a tough combination of loads: it is compressed between the bolt shank and the flange bore, it is dragged into position during assembly, and it has to stay electrically continuous through the whole service life of the line. A rigid material like phenolic can crack during installation or under torque; Mylar flexes without cracking, which is why it is the most widely specified sleeve material on cathodically protected pipelines worldwide.
- MaterialBiaxially oriented polyester (PET) film — the material most widely recognised as "Mylar" in the pipeline industry.
- Dielectric strengthExcellent for the film thickness used, providing predictable electrical isolation across the bolt hole.
- Water absorptionVery low — dielectric properties stay stable in wet, humid and buried service.
- Mechanical durabilityStronger than phenolic in the specific role of bolt-hole isolation; far less prone to cracking during torquing or installation.
- Fit toleranceSlides over the flange bolt with a small clearance so it fits standard bolt and bolt-hole combinations, even with some misalignment.
Where the Sleeve Sits in the Insulation System
Insulating a flanged joint requires breaking every current path through the connection. In a fully insulated joint that means three dielectric components working together — and if any one of them is missing, the isolation fails.
At the flange face. Breaks the face-to-face path. Type D, E or F geometry depending on the flange standard.
Through each bolt hole. Slides over the bolt shank so the shank cannot contact either flange plate. Used together with G-10 / G-11 or phenolic washers.
Under each nut and under each bolt head. Typically G-10, G-11 or phenolic.
Extended-length sleeves, secondary washers and non-standard diameters available as custom-cut items.
Sleeves are supplied in standard wall thickness and are designed to be used with separate insulating washers — they are not sold as a combined sleeve-washer unit.
Mylar vs Phenolic vs G-10 — Sleeve Material Selection
Three sleeve materials are commonly specified in the industry. The choice depends on the joint's operating conditions and the buyer's installation experience with each material.
Recommended as the industry-standard bolt-hole sleeve. Survives torque and installation without cracking.
- High dielectric strength
- Very low water absorption
- Flexes rather than cracks
- Fits with some misalignment
- Standard metric and imperial
Used for higher-temperature joints and where the sleeve must also carry structural load. See insulation sleeves.
- High mechanical strength
- Good dielectric strength
- Higher temperature capability
- Supplied custom-machined
Older alternative — more brittle than Mylar and can crack during installation. See phenolic sleeve.
- Standard electrical insulation
- Lower cost
- More brittle than Mylar
- Higher risk of cracking
Technical Data — Mylar Insulating Sleeve
| Property | Typical Value | Notes |
|---|---|---|
| Material | Biaxially oriented polyester (PET) film | Industry-standard "Mylar" |
| Dielectric strength | High for the film thickness | Core insulation property for bolt-hole isolation |
| Water absorption | Very low | Stable electrical performance in wet and buried service |
| Standard wall thickness | Single wall | Used with separate insulating washers |
| Standard length | 900 mm / 3 ft | Full length or cut to specific bolt length |
| Available diameters | Standard metric and imperial bolt sizes | Custom non-standard sizes on request |
| Fit clearance | Small clearance over bolt shank | Fits standard bolt-hole combinations even with slight misalignment |
| Installation compatibility | Used with G-10 / G-11 / phenolic washers | Sleeve alone does not complete the isolation |
Typical B2B Applications
Ordering Mylar Insulating Sleeves
Sleeves are supplied in full 900 mm / 3 ft lengths or cut to your specified bolt length. Send the following five details and Kaxite will return a quotation — typically within one working day for standard sizes.
Mylar Insulating Sleeve — FAQ
What is a Mylar insulating sleeve made from?
Mylar is a biaxially oriented polyester (PET) film. The sleeve is formed from this film and used as the bolt-hole dielectric in a flange insulation kit. Mylar is the most widely recognised sleeve and bolt insulating material in the pipeline industry, and has excellent dielectric strength and very low water absorption.
Why choose Mylar over phenolic for the sleeve?
Mylar is stronger than phenolic in the specific role of bolt-hole isolation and far less prone to cracking when the flange is torqued or the sleeve is bent during installation. Phenolic is more brittle and can crack under the same conditions. For most pipeline joints Mylar is the safer sleeve material to specify.
How does the sleeve fit into a flange insulation kit?
A fully insulated joint has three dielectric components: the gasket at the flange face, the sleeve through the bolt hole, and the washer under the nut (and typically under the bolt head). The Mylar sleeve is the second of these — it slides over the bolt shank so the shank cannot contact either flange plate. Removing any one of the three components will cause the isolation to fail.
Can Mylar sleeves be cut to a specific bolt length?
Yes. The standard supply length is 900 mm (3 ft). Sleeves can be supplied in full lengths for cutting on site, or cut to your specific bolt length at the factory. Send the finished sleeve length and quantity required.
Are Mylar sleeves compatible with G-10 and G-11 washers?
Yes. Mylar sleeves are designed to be used with separate insulating washers such as G-10, G-11 glass epoxy or phenolic. The sleeve and the washers together complete the isolation. If you need a matched set from one supplier, send the flange standard and size and we will quote them together.
Do you supply Mylar sleeves in metric and imperial sizes?
Yes. Sleeves are supplied in both metric and imperial bolt diameters. Custom non-standard inside and outside diameters are produced to order — send the dimensioned drawing and we will confirm feasibility and lead time.
What quantity is required for OEM / wholesale pricing?
OEM and wholesale pricing applies from the first order for standard sleeve sizes, and from 500 pieces per size for custom-cut sleeves. Send the annual or project quantity and we will quote the volume tier.
What is the lead time for Mylar sleeve orders?
Standard sizes ship from stock or on short lead time — typically 5–10 days depending on quantity. Custom-cut lengths or non-standard diameters are produced to order, generally 10–20 days. Send the specification for a confirmed delivery schedule.
Request a Mylar Insulating Sleeve Quotation
Send the bolt diameter, sleeve outside diameter, length and quantity — or the flange standard and size for a complete kit quotation. Kaxite supplies Mylar sleeves for OEM flange insulation kits, maintenance replacement, and standalone bolt-hole isolation on cathodically protected lines.