Webasto or Espar - Eberspacher Thermoduct Tube for 75/100mm Ducting 

Suitable for 75mm-100mm ducting | Comes in 750mm length pieces | Suitable for Marine and Vehicle use | Thermoduct is 19mm Thinsulated which is resistant to damp and water ingress, and is covered by a strong, hard wearing fabric with closed end stitching | This Product will increase the heating performance, by reducing the heating up time, therefore giving better fuel and electrical economy | Tests confirm that up to 40% of the heaters output can be lost through the ducting. Heat is retained within the ducting air flow to reach the desired areas of the boat. It can eliminate condensation and prevent the warming of food 

Fitting Instructions: 
Please note, before sliding the APK ducting inside the sleeve, you will need to tape up the end of your ducting, to get rid of any sharp edges or even a sock like cloth, then the ducting will slide freely inside without ripping the tube.