For hot pipe in the 300F to 1200F range, three materials cover most of the field: cal-sil, expanded perlite, and rock wool. They overlap enough that people treat them as interchangeable, and they are not. Picking the wrong one usually does not fail on temperature. It fails on strength, moisture, or budget. Here is how they compare.
Cal-sil is the strong one. Rock wool is the light, cheap, easy one. Perlite sits between them and gets picked when moisture resistance and strength both matter. All three handle high heat. The difference is everything else.
Rigid block and pipe covering, rated to 1200F, with high compressive strength. That strength is why it gets specified. On piping that gets walked on, near grade, on fittings that take abuse, or under jacketing that sees foot traffic, cal-sil keeps its shape where a softer material would crush and lose its thermal value. Heavier and pricier than rock wool, so it goes where it earns that cost, not blanket-applied across a whole unit. It will absorb water if it gets wet, so the jacket matters. Keep it dry and it lasts for decades.
Also rigid and rated into the 1200F range. Its edge over cal-sil is moisture behavior. Many perlite products are treated to resist water absorption and wicking, which makes them a good fit where the line runs outdoors or in a wet area and still runs hot. Good compressive strength, though the numbers vary by product. Where a spec worries about both crush resistance and water, perlite is often the answer.
Rock wool, also called mineral wool or stone wool, comes as preformed pipe covering and as blanket and board. Rated to around 1200F depending on the product. Lighter than the other two, cuts and fits fast, costs less. On long straight runs of hot pipe that will not get abused, rock wool is usually the economical choice and the one crews prefer because it goes quickly. What it gives up is compressive strength: it compresses more easily than cal-sil or perlite, so it is not the pick for high-abuse spots or where something bears on it.
Think trade-offs, not a ranking. If the deciding factor is crush resistance, go cal-sil. If it is moisture plus strength, look at perlite. If it is cost and speed on protected runs, rock wool. Temperature ceiling rarely decides among these three, because they all reach into the same high range.
On a lot of Permian gas processing and power jobs, the same unit uses more than one. Cal-sil on the low elbows and walk-over points, rock wool on the long elevated runs, perlite where a hot line sits out in the weather. The spec often names the material per service, and the estimator reads which is called where and prices accordingly.
Confirm three things off the spec: the material and grade (a C533 Type I cal-sil is not the same order as a C547 fiber product), the temperature and thickness from the thickness table, and the jacket system, because a moisture-sensitive material like cal-sil leans hard on its jacket. Get those right and the material list writes itself.
Both handle high heat, but they solve different problems. Cal-sil is rated to 1200F with high compressive strength, so it wins where the insulation takes abuse or has to hold its shape. Rock wool is lighter, faster to cut and fit, and usually cheaper, so it wins on long runs where abuse is not a concern. Many plants use both, cal-sil where it gets stepped on and rock wool everywhere else.
Yes. Expanded perlite is specified for high-temperature service and valued for its strength and its resistance to moisture wicking. It competes directly with cal-sil in the same temperature range, and the choice often comes down to what the spec names and what is available on the timeline.
As a rough guide, all three reach into the 1200F range: rock wool pipe covering, cal-sil, and expanded perlite. The real difference at the top of the range is compressive strength, moisture behavior, and weight, not the temperature ceiling.
Yes. Send the insulation section of your spec and the takeoff. We confirm which material the spec requires, check stock at the nearest branch, and return a priced list the same business day.
We stock the material and price it the same business day.