Johns Manville Pipe Insulation and Duct Wrap Data Sheet: An Open FAQ

I'm a quality and brand compliance manager at Johns Manville. I review product documentation and sample deliveries before they reach contractors—roughly 200 unique items annually. A lot of people treat a data sheet as a formality. It's not. The data sheet is a contract, and every number on it is spelled out.

Below are the questions I actually get from contractors, distributors, and specifiers. I answered them the same way I'd answer an email: straight, with the caveats included.

What is Johns Manville pipe insulation used for?

Johns Manville pipe insulation is a pre-formed fiberglass insulation for hot and cold piping. I review it for hydronic heating, chilled water, steam condensate, and plumbing supply lines. It comes in sections sized to fit nominal pipe diameters, usually with a factory-applied jacket. The jacket protects the fiberglass and acts as a vapor retarder. If the jacket tears or the section doesn't fit, moisture gets in and the performance drops.

When I approve a pipe insulation spec, I check three things first: inner diameter, wall thickness, and jacket type. The R-value matters, but not if the section is loose on a 3-inch pipe.

What should I look for on the Johns Manville duct wrap data sheet?

The current Johns Manville duct wrap data sheet is the PDF you find in the JM product library. It lists roll dimensions, thickness, R-value at the mean temperature stated on the sheet, facing type, and flame/smoke ratings. I check the revision date every time. A data sheet from last year might not reflect the current product listing.

Put another way: if the project spec says to follow the manufacturer's published data sheet, the published sheet has to be the current one. Not a screenshot from an online search result. Not the number on a distributor's price sheet.

From the JM product library (accessed March 2025): the duct wrap data sheet is the authority for R-values, facings, and code listings. If it isn't listed, it isn't approved.

Which facing should I choose: FSK, PSK, or ASJ?

FSK means foil-scrim-kraft. PSK means polyester-scrim-kraft. ASJ is an all-service jacket. They are not interchangeable. On duct wrap, FSK is common because the foil layer acts as a vapor retarder and reflects heat. On pipe insulation, ASJ is the usual white jacket you see in mechanical rooms. If you use FSK where the spec calls for ASJ, you change the vapor permeance and the surface finish. That is a specification issue, not a preference.

I had a vendor tell me once that they were both just jackets. That was the last time we accepted an unverified substitution.

Can I use Johns Manville pipe insulation on ductwork?

No. It looks like similar fiberglass, and sometimes it is made in the same family of products, but pipe insulation is formed into circles for a reason. Ductwork has flat surfaces and square corners. A round section leaves a gap along every flat run. If you crush the fiberglass to force it against a duct, you remove the air pockets that provide the insulation value. The correct product for sheet metal ducts is duct wrap or duct board.

What I mean is: the shape of the insulation is part of the specification. Don't substitute based on material alone.

How do I know if Johns Manville pipe insulation is the right spec for my project?

No insulation is the best everywhere. Johns Manville pipe insulation is a good fit for most commercial piping systems within the temperature limits on its data sheet. If you need a product for a below-grade chase that routinely sees standing water, a closed-cell foam is probably a better fit than fiberglass. If you need a continuous operating temperature above the JM data sheet limit, mineral wool or calcium silicate should be considered.

If your project is a standard hydronic or chilled-water piping job, JM pipe insulation will do what it says on the sheet. Here is how to know if you're in the other 20%: the design condition is outside the listed limits, or the engineer's specification names a different product standard.

What quality problems do you catch before products ship?

I review a lot of deliveries, and I reject a small percentage every year. In Q1 2024, I rejected 400 linear feet of pipe insulation because the inner diameter was oversized by about 1/16 inch. The vendor said it was within industry standard. But our approved data sheet allowed a tighter fit, and the project's insulation inspector flagged the gap. The vendor redid it at their cost.

The most common issues I catch are wrong facings, wrong inner diameters, missing roll identification, and labels that don't match the actual product. A label is not a quality check.

What about a toilet fill valve or how to install bathtub faucet?

If you came looking for a toilet fill valve replacement, or if you searched for how to install bathtub faucet, this page is not a plumbing fixture tutorial. I'm not a plumber, so I can't walk you through a valve install. What I can tell you from an insulation perspective is simple: if you are opening up a wall to do either job, use the opportunity to insulate the exposed supply lines.

A toilet fill valve itself is not a Johns Manville product. A bathtub faucet is also not a Johns Manville product. But the hot and cold lines behind that faucet can sweat, lose heat, or pick up noise if they run through a cold chase. That is where pipe insulation—the right ID, with a sealed jacket—comes in.

What does white crop top have to do with Johns Manville?

Nothing. That is almost certainly a search suggestion mix-up. If your search actually says white crop top, the page you need is somewhere in the fashion section. If you meant a white rooftop or a white top membrane, then Johns Manville makes white single-ply roofing membranes and white insulation jacket materials. Those are building products, not clothing.

Search engines cluster words, not intent. The same query that brings you to a pipe insulation page can also show clothing results. The important thing is to check the search terms against your project drawing. If you see a clothing term on a purchase order, stop and verify.