Mineral Wool vs Recycled Plastic Insulation

Two ways to insulate a loft floor

If you are choosing a quilt-type material to lay across a loft floor, mineral wool and recycled plastic are the two you are most likely to weigh up. Both are rolled insulation, both trap air to slow heat loss, and both are installed in much the same way — a layer between the joists and a thicker layer across them. The differences are less about headline performance and more about handling, feel, cost and priorities. Here is an even-handed comparison.

Handling and comfort

This is where the two feel most different in practice.

Mineral wool — glass or rock — is made of fine mineral fibres. It performs reliably and is inexpensive, but during handling those fibres can irritate skin, eyes and airways, so installers use gloves, eye protection and a mask. For a homeowner working in the loft, it can be itchy to deal with.

Recycled plastic insulation, typically made from polyester fibres including recycled bottles, is generally softer to handle and non-irritating, with no loose mineral fibres. Many people find it more pleasant to work around, which is a genuine consideration in a loft you will visit for storage or maintenance.

Cost

Mineral wool is usually the lower-cost option, which is a large part of why it is the default material for most loft-floor work in the UK. Recycled plastic quilts tend to sit at a higher price point. Neither is expensive relative to the value of a well-insulated loft, but if budget is the deciding factor, mineral wool typically wins on price. The right comparison is always for the specific products and depths being quoted.

Sustainability

Both materials have a recycled-content story. Recycled plastic insulation is often chosen precisely because it reuses plastic that might otherwise be waste, and it appeals to households prioritising that. Mineral wool also contains recycled material — recycled glass in the case of glass wool. Rather than assume one is greener, it is worth looking at the individual product’s recycled content, how it is made and what happens to it at end of life. The Energy Saving Trust offers general guidance on insulation that can help frame the choice.

Thermal performance

Here the honest answer is that both perform well, and the material category matters less than the product and the depth. Thermal performance is set by the specific quilt and how deep it is laid, confirmed against the data sheet, not by whether it is wool or plastic. For wool, 270mm is the commonly used benchmark; recycled plastic quilts have their own specified build-up. Installed correctly to the right depth, either will insulate a loft floor effectively.

Moisture and fire

Both are breathable quilts that should be kept dry and never compressed under boarding. Their fire classifications differ by product, so this is checked on the individual data sheet rather than assumed. As with any loft, ventilation matters as much as the material: insulation and airflow are considered together so moisture is not trapped at the eaves.

Which suits which loft

For most straightforward lofts — including many post-1965 homes — mineral wool is the sensible, economical default and the usual choice for a loft insulation installation or a top-up. Recycled plastic is worth the extra outlay where softer, non-irritant handling matters to you, where the loft will be worked in often, or where its recycled-content story aligns with your priorities.

The honest bottom line

There is no single winner. Mineral wool offers proven performance at the lowest cost; recycled plastic offers easier handling and a recycled-plastic sustainability angle at a higher price. Both insulate a loft floor well when installed to the correct depth. The right choice depends on your budget, how much you value comfortable handling, and what matters to you environmentally — which a survey can help you weigh for your own loft.