Indoor / outdoor carpet is generally mfg. from polypropylene .
1) the colour is put in before it becomes a woven fibre / so it is a carrot not a radish = resistant to fading .
2 ) the form used in carpet fibre does not absorb moisture , which makes it highly mold and mildew resistant.
3) UV rays can eventually cause changes in colour if exposure is 24 / 7 ;and I believe can eventually lead to the fibre becoming more brittle . ( think- boat dock yellow rope that floats / it is made from polypropylene).
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I have 2 indoor/ outdoor rugs that are inside our cottage that we close up all winter . I bought them
because of the mildew / mold resistance - and cleanability (and moderate $ price) . When we want to do a “spring cleaning “ - I bring them outside and hose them down , and then let them dry .