Insulation Knife Fiskars 420 mm model 125870 for mineral wool cutting

Fiskars insulation knife 420 mm model 125870 is a purpose-built cutting tool for trimming and shaping mineral wool insulation. The long, straight blade offers a cutting length suited to insulation mats and batts, enabling smooth, even edges for installation in walls, roofs and floors. The tool is designed for both professional installers and DIY users who need accurate, efficient cutting of fibrous insulation materials.

Advantages

The long blade design reduces the number of passes required to cut wide insulation panels, improving work speed and consistency. The knife construction provides good control and straight-line guidance, helping to achieve clean edges that fit tightly into framing and junctions. The tool is lightweight and easy to handle during extended use, and its shape minimizes tearing or compression of mineral wool, which preserves insulation performance.

Suitable for

• Trimming mineral wool mats and batts to fit wall cavities
• Cutting insulation for roof and loft installations
• Shaping insulation for floor and suspended ceiling projects
• On-site adjustments during renovation and retrofit work

Key specifications

• Blade length: 420 mm cutting length suitable for standard insulation panel widths
• Intended material: mineral wool (glass wool, rock wool) and similar fibrous insulation
• Handle design: ergonomic for two-handed guidance and improved straight cuts
• Construction: lightweight tool designed for manual cutting of insulation

How to use

Mark the desired cutting line on the mineral wool with a straightedge or marker. Position the blade along the line and apply steady, even pressure while sliding the knife through the insulation. For thicker batts, use a single continuous stroke where possible or perform a shallow scoring pass followed by a full cut to reduce distortion. Maintain a firm grip on the handle and support the insulation to avoid compressing the material during cutting.

Usage recommendations

Wear appropriate personal protective equipment such as gloves, long sleeves and a dust mask when cutting mineral wool to reduce skin irritation and inhalation of fibers. Keep the blade clean and replace it if dull to ensure straight, efficient cuts. Store the knife in a dry place and transport it with a blade guard or sheath to prevent damage and accidental contact.