What are the differences in grinding performance between open-coated sandpaper and closed-coated sandpaper?

The differences in grinding performance between open-coated sandpaper and closed-coated sandpaper mainly show up in the following parts:

Grinding efficiency and speed:
Closed-coated sandpaper: Because the abrasive grains are tightly stuck together and the abrasive particles basically cover the backing completely, the contact area with the workpiece is larger when grinding. So, the grinding efficiency is usually higher and the grinding speed is faster.
Open-coated sandpaper: The gaps between the abrasive grains are relatively big and only about 1/3 to 3/4 of the abrasive is used in each area. This makes the contact area with the workpiece smaller. So, the grinding efficiency might be a bit lower and the grinding speed will be slower.

Durability and clogging resistance:
Closed-coated abrasive paper: Since the abrasive grains are arranged closely, the debris produced during grinding is easy to pile up between the grains. That makes the abrasive paper clog easily and it affects the grinding effect and durability.
Open-coated abrasive paper: The gaps between the abrasive grains give a way for the debris to get out. This makes it easier for the debris to be removed and reduces the chance of clogging. This makes the abrasive paper more durable. Especially when dealing with materials that are easy to clog, like softwood with a lot of resin or grease, open-coated abrasive paper does better.

Applicable scenarios and materials:
Closed-coated abrasive paper: Because it has high grinding efficiency and is fast, it's more suitable for grinding hard surfaces or situations where a lot of material needs to be taken off quickly, like grinding metal and rough processing.
Open-coated abrasive paper: Because it's not easy to clog and is durable, it's more suitable for grinding soft surfaces or materials that are easy to clog, like softwood with resin and painted surfaces. Also, open-coated abrasive paper is better for grinding curved surfaces and fine grinding.

User experience and comfort:
Closed-coated abrasive paper: Because the abrasive grains are arranged closely, it might create more friction and heat when you use it. This can have an effect on how comfortable it feels for the operator's hand.
Open-coated abrasive paper: Because the gaps between the abrasive grains are larger, the friction and heat are relatively smaller. So, it's more comfortable to use. At the same time, open-coated abrasive paper is also easier to fold and reuse, which improves the use rate of the material.

Open-coated abrasive paper and closed-coated abrasive paper both have their good and bad points in grinding performance. When choosing, you need to decide which type of abrasive paper to use based on the specific grinding needs, the characteristics of the materials and the situations.