First, establish what you want to protect your car from. Here is an overview of the possible risks, in which storage locations they may occur, and the features that a cover should have to protect your car from them.
RISK
- where may it occur?
required feature
DUST
- anywhere
dust tight
SCRATCHES
- anywhere
soft
sturdy
non-scratchy
inner lining
soft on paint
to protect from scratches by sharp edges on zippers, garden tools, bikes etc.
If a car cover does not fullfil all of the above requirements, there is no point in using it.
But, depending on the storage conditions there may be additional risks,requiring extra features from the car cover:
RISK
- where may it occur?
required feature
UV-RAYS
- outdoors
- carport
- indoors when parked near
window or under glass roof
UV - resistant
CONDENSATION
- outdoors
- carport
- indoors in
unheated space
breathable
to allow moist to escape when it evaporates
RAIN
BIRD/TREEDROPPINGS
- outdoors
- carport
water tight
