This depends on the fabrics you have chosen. We do a wide range of waterproof fabrics which will be waterproof and our polar fleece is wind and rain repellent but not completely waterproof.
Please always use a raincover as it has been suggested that something in the rain could make the colours in your footmuff fabric run, whereas it doesn't run in a wash cycle. We don't know how true this is but we have had one case reported of a footmuff fabric 'apparently' running in the rain, but tests at our workshop using cold water, warm water, boiling water and a 30 degree wash, with vigorous scrubbing afterwards were unable to reproduce any form of colour run or bleed on the same fabric.
All of our footmuffs are machine washable at 30 degrees, on their own, and with AT LEAST 1 colour catcher but use more if strong colours are used together.