For cheap insulation, put bubble wrap on your windows to help keep the heat in. Just spray them with water and the bubble wrap will stick to the window. : r/Frugal
Bubble Wrap [Your Complete Guide] | Springpack UK
Stay Away from Foil-Faced Bubble Wrap - GreenBuildingAdvisor
What is Bubble Wrap Insulation?
Double Aluminium Layer Bubble Wrap Foil Insulation Roll Self-Adhesive Heat Retention and Energy Saving Radiator Insulation Foil(Size:1×20m) : Amazon.ca: Tools & Home Improvement
The Truth Why is Bubble Wrap a Good insulator for Windows?
9 Uses for Bubble Wrap - Bob Vila
The Truth Why is Bubble Wrap a Good insulator for Windows?
A Guide to Bubble Wrapping a Greenhouse - Hartley Botanic