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There are different types of weatherstrip that fall into several general categories, but for the most part they all have the same purpose: to fill a gap somewhere and create a thermal and moisture barrier.

The most common materials are solid foam, hollow bulb, and wool pile brush, which usually comes with a moisture barrier fin at it’s center, and which we call fin-seal.

The most common types are slot in, kerf in, and adhesive backed.


This is the kind of slot these strips go into.

There are many other widths, these two are among the most common.

This one’s hollow bulbslot in.

This is the wool pile weatherstrip. It’s also called brush weatherstrip, and may or may not have a plastic fin in the middle of the pile.


That’s the fin in fin-seal, and it does a lot of the work in the moisture barrier department. You can always sub finned for non filled pile weatherstrip. It works in a slot, like the others.


The adhesive version of these would look the same, but the part at the top would be coated with adhesive and covered with a tape until installation. You would not need a slot for these; they would attach to any flat dry surface.


This is a hollow bulb with a kerf. That arrow-like anchor is the kerf. Foam and wool pile weatherstripping can have a kerf, too.


The good news is that you can freely mix and match among these materials to come up with something that will meet your immediate needs.

If you find a fin seal with the right backing and a pile height that matches the height of a bulb seal you need, go ahead and use it!

There are differences in the thermal properties and water resistance among these materials, but they all do a decent job, and when the exact ideal perfect seal is not available, a functional sub is much better than leaving a gap, which will eventually cause the loss of the door or window.

There are some rules, though.

A seal that’s fractionally larger in the bulb diameter/pile height dimension (.320 for .290”, for instance) will generally not be a problem. You should not sub with anything smaller than the existing seal.


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