Very hard to get any kind of quality with them in there. If they rip and drop while filling, even worse. Compressing the existing will negate it and adding another won't give you the R-value as if it wasn't there. If the old is faced, it should be to the warm in winter side if in a cold climate. Using dense-pack cellulose may work better, if done by a professional.....
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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?