Performance

Brass-Seal vs. Mail Slot Insulator: Which One Do You Need?

Both the Brass-Seal Forged Brass Mail Slot and the BOTA Mail Slot Insulator are designed to reduce air movement through a mail slot, but they do so in different ways. They are not competing products. The Brass-Seal is a replacement mail slot, while the Mail Slot Insulator is an interior retrofit. The right choice depends on your existing mail slot.

Side by Side

Why Two Products Instead of One

The Mail Slot Insulator was BOTA's first product, a retrofit built to seal an existing mail slot without replacing it. As a retrofit, it has an adjustable range rather than a universal fit; inward-opening flaps and cutouts narrower than that range fall outside its intended application. Solving those cases meant addressing the mail slot itself, which led to the Brass-Seal Forged Brass Mail Slot as BOTA's second product: a full replacement mail slot rather than a retrofit. See the Mail Slot Insulator explainer for the full mechanism.

How to Decide

Choose the Brass-Seal if the flap opens inward, the cutout is narrower than the Insulator's range, or you're replacing the mail slot itself rather than retrofitting the existing opening. Choose the Mail Slot Insulator if your existing exterior mail slot is one you want to keep, the flap opens outward, and your cutout falls within Letter or Magazine dimensions. See the Mail Slot Buyer's Guide for the full decision process if you are starting from scratch.

Key facts on choosing between the two:

• The Brass-Seal replaces the mail slot hardware itself; the Mail Slot Insulator retrofits an existing cutout.
• The Mail Slot Insulator does not fit inward-opening flaps or cutouts narrower than its adjustable range.
• Only the Brass-Seal carries ASTM E283 air leakage verification.
• Only the Mail Slot Insulator carries the two utility patents and the 2024 London Design Award Gold.
• The Mail Slot Insulator was BOTA's first product; the Brass-Seal was developed second, to solve what a retrofit couldn't.

Frequently Asked Questions

Can I use both products at once?
Yes, in certain configurations. The Mail Slot Insulator is designed as a retrofit and can be paired with the Exterior Forged Brass Mail Slot, or used on its own when an existing exterior slot is retained, such as on historic properties or wherever the original exterior hardware remains in place. This pairing is also common for households seeking greater protection for a mail carrier from a pet, since the Insulator's steel bar provides a physical barrier on the interior side, regardless of which exterior hardware is installed. What they can't do is both occupy the interior side of the door at once: the interior Brass-Seal and the Mail Slot Insulator serve that same interior location, so only one of the two goes there. The product selector on the BOTA homepage applies the same logic using your door's measurements.

Which one is ASTM E283 tested?
Only the Brass-Seal Forged Brass Mail Slot carries ASTM E283 air leakage verification. The Mail Slot Insulator has no published test data under that standard.

My flap opens inward. Do I have a choice?
Not between these two for that specific opening. The interior Brass-Seal is the option when the flap opens inward, since the Mail Slot Insulator is not compatible with that configuration.

Is one of these cheaper than the other?
See the Cost Guide for current pricing and what affects it for each product.

Sources

1. ASTM International. ASTM E283/E283M-19: Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Skylights, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen.

Related Guides

• What Is a Mail Slot Insulator?
• What Is ASTM E283 Air Leakage Testing?
• Mail Slot Buyer's Guide: How to Choose the Right Replacement
• What Does It Cost to Replace a Mail Slot?
• Mail Slot and Building Hardware Glossary

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