To introduce insulation to the humble Wellington Boot you need to embrace the latest Technologies. Grubs Boots have done just that and have produced a wide range of boots with two levels of insulation.
This provides a boot intended for comfort from Autumn through to Spring. They can be used in Summer, but you could end up with hot feet! Temperature range being -20ºC to +20ºC
This provides a boot that will be comfortable for sustained use in extreme temperatures down to -40ºC, but the offset with all this insulation is the boots could be too warm for use above 15ºC
You have to mindful the comfort ranges are only a guide. Some people have colder feet than others, so the 8.5 rating may be appropriate for use most of the year. You really need to try the boots to assess how good they are.
Another point associated with the design of an insulated boot is the acknowledgment that in colder weather we all tend to wear thicker trousers. Grubs Boots use of insulating foam in the upper allows the boot to stretch to accommodate thicker trousers and still retain the comfort level.
The level of insulation will be one of the determining factors in choosing your next pair of wellington boots, but the other issue will be the selection of an appropriate sole pattern for the intended use. Grubs have the largest selection of sole patterns and you are sure to find one for your intended use