I like this product for the big peace of mind at modest cost. It's almost impossible to be 100% certain you got all the sharp, poky things out of the dirt but this felt takes care of that. Plus your knees will thank you when you forget your knee pads. The added thickness is a real plus and shows this company cares about quality and continual improvement. One last benefit: if you ever need to deal with radon gas, the felt makes a great air transfer layer u dear the vapor barrier.

We have recently used the 42 5100 under our 20 MIL liner and I will have to say it's a must. We will be using this product under our crawlspace liners from here on out.

1) GOOD: This is not like roofing "42" , and shouldn't be. 42 has an organic fiber base which will decay if continuously wet, as underneath a vapor barrier. This synthetic product is just what is needed as a vapor barrier underlayment. 2) OK: I got this to protect my vapor barrier from sharp-edged gravel which was already covering my crawlspace floor. As such, this product is OK, but not as thick as I expected. It is like an extra-thick landscape fabric.

This is some really good durable stuff.

Product is of good quality