Word meaning vulnerable to the elements

could you be looking for pervious and impervious?

As adjectives the difference between pervious and impervious is that pervious is admitting passage; capable of being penetrated by another body or substance; permeable while impervious is unaffected or unable to be affected by.

or simply

Weatherproof

Resistant to the effects of bad weather, especially rain.

susceptible works, although that doesn't exclusively refer to susceptibility to the elements.

From Merriam Webster:

susceptible - adjective - sus·cep·ti·ble \ sə-ˈsep-tə-bəl \ - 1 : capable of submitting to an action, process, or operation a theory susceptible to proof

2 : open, subject, or unresistant to some stimulus, influence, or agency susceptible to pneumonia

3 : impressionable, responsive a susceptible mind

— susceptibleness noun

— susceptibly adverb