Is Rockwool Harmful? Yes, But…
Rock wool has long been a popular media for growing hydroponic fruits, vegetables and herbs. However, I’m going to make the case against rockwool and argue why you should never use rockwool again because rockwool is harmful

This post has gotten a lot of attention recently, and as a result is in the process of being updated to include more information. I cite studies and in no way reference any particular company – I am talking about mineral wool as a growing media in this post.
If you want better alternatives to rockwool, please check out my hydroponic media guide.
It’s Not Environmentally Friendly
I believe in environmental sustainability – it’s one of the reasons I’ve chosen to grow hydroponically. Rockwool doesn’t score well on the environmental scale. It’s not a natural material. Manufacturers use combine chalk and rock and then heat them up to around 3,000 degrees Fahrenheit. Next a stream of air is blown through it, resulting in extremely thin fibers of the rocky material. As the strings are blown out, they bunch together and form the material that you see for sale at the local hydroponics store.
Basically, they are taking two materials that are 100% natural (chalk and rock) and turning them into a hybrid material that will remain in that form forever. When you throw away your old rockwool it’s going to sit in a landfill looking just like that for a long, LONG time. If you absolutely insist on using it, try to save your rockwool in between your growing season and reuse it.
It’s Not Healthy To Be Around
Not only is rockwool unfriendly to the environment – it’s also potentially harmful to your health. New blocks can contain a lot of dust and loose fibers that can get in your eyes, mouth, skin and lungs. It’s similar to asbestos in the sense that the little fibers can lodge themselves in your lungs if you’re working with it a lot. It may not be as toxic as asbestos, but why take the risk? Not something that I’m willing to gamble with if I don’t have to – there are plenty of other hydroponic media choices! If you’re using rockwool, you should be using a mask, goggles and gloves when you work with it to protect yourself.
Ceramic fibers
Ceramic fiber was designed and developed for applications in which the composite matrix/resin temperature can go, for example, as high as 1000°C in a corrosive and oxidizing environment.
The ceramic fibers are made from precursor fibers or a very thin tungsten-core wire. Materials like boron and silicon carbide vapors are deposited onto a red-hot precursor moving very slowly. Some of the ceramic fibers are large-diameter monofilaments.
The ceramic fibers show high-strength and high-modulus properties in both tension and compression applications. In compression, unidirectional boron composite stress–strain curves are linear to failure (400,000 psi failing stress) and exhibit a modulus of 30 million psi.
Because ceramic fibers have large diameters, prepreg tapes formed from the fibers are usually unidirectional only.
The ceramic fibers are uniquely suited to handle the high-temperature consolidation conditions of titanium and ceramic matrix composites. Only limited quantities of ceramic fibers are manufactured annually but production can be rapidly expanded to meet new demands.
Bio-soluble fiber paper SUNTHERM HB （Bio-soluble） Fiber Paper
is a new develop at the basic of the traditional ceramic fiber, the main components is MgO, CaO, and contains a small amount of organic binder, with integrated fire resistance, heat separation and thermal insulation functions, can be used at higher temperatures filed, bio-soluble fiber can replace part of the traditional ceramic fiber, the use of temperature can reach 1050C, and have excellent eco-friendly performance.
Applications
?Furnace expansion joint filler
?High temperature gasket
?High-temperature insulation backing
?Fire protection facilities
?Molten metal splash protection
?High-end household appliances insulation device
Features
?Easy twisting, shaping and cutting
?Excellent machining performance
?Excellent tensile strength
?Acoustic performance
?Good anti-spalling properties
?Low thermal conductivity, low thermal capacity
?Resistance to wind and erosion, long service life
?Excellent thermal insulation, fire protection,
thermal insulation and acoustic performance
What is Ceramic Fiber Bulk?
Ceramic Fiber Bulk is a high temperature refractory insulation material manufactured from high purity alumina and silica raw materials on computer-controlled furnaces to provide consistent fiber properties. Fibers are lightweight, chemically inert, and have all the positive characteristics of ceramic fiber. Bulk insulation is the perfect solution for insulating intricate spaces, parts, or shape forming for various commercial and industrial applications. Our office currently stocks “spun” ceramic fiber bulk rated for temperatures up to 2300o F and 2600o F. If a different temperature rating or grade is needed, please contact our office directly for a custom quote.
Blown vs Spun vs Chopped Fibers?
In addition to varying temperature grades, Ceramic Fiber bulk is available in blown, spun, or chopped fibers. Blown fiber has the smallest fiber size and is more flexible in comparison to the other grades. Spun fiber is very similar to blown, with the exception of longer fibers and a greater rupture / tensile strength. Spun fiber is still light and airy in appearance and is the most commonly used fiber in applications. Chopped fiber has the largest fiber size and is bulky in appearance. Our office currently stocks spun fiber but if another grade is required, please contact us for a custom quote.