I am looking at two REI Co Op tents. One has a Polyester canopy and one has a Polyester/Nylon Canopy. Can you please explain to me the differences?
Not an REI employee but...
Because it available in finer weaves Nylon is generally used for light weight backpacking tents. The disadvantage of nylon is that it adsorbs water and tends to sag so it is not generally used for larger tents.
Polyester is innately hydrophobic and does not sag when wet but the heavier weaves it comes in make for a heavier tent so it is generally only used for less expensive small tents and for larger tents where nylon is not practical.
Another aspect is the waterproof coating. Less expensive tents use an PU coating where Silicon in generally used for the more expensive lightweight tents. Some tents use Silicone on the outside and PU on the inside. Silicone tend to be last longer and is much less prone to mildew. However it is harder to work with and to seam seal than PU I think because you can only seal it with silicone.
An nylon polyester blend is not a common tent material as far as I know and does not jump out has having any particular advantage unless it allows a lighter weave but doesn't sag as much when wet. In practice I doubt it makes much difference vs a Polyester fabric and I would choose the tent based on your budget and the suitability of the tent design to you need.
Since you don't say which tents you are looking at it is hard to say anything more specific
@FireRunner Thanks for reaching out with this question!
@OldGuyot is spot on in their analysis and answering of your question. We would just emphasize that it would be helpful to know which tents you were looking at, as the benefits of each (polyester and nylon) come in to play with a tent's end use (i.e. Backpacking vs Car camping, or ultra lightweight, etc.).
Hopefully this helps, thanks!