Is the Serta Onyx Firm good for side sleepers?

Probably not. It is a firm innerspring with little cushioning, so side sleepers often feel pressure at the shoulder and hip. A mattress topper helps, but a softer model suits side sleepers better.

How firm is the Serta Onyx Firm?

It is genuinely firm, with a traditional coil feel and minimal foam on top. Back and stomach sleepers tend to like it; side sleepers and light sleepers often find it too hard.

What size is the Serta Onyx Firm Twin?

It is a standard twin, about 38 by 75 inches, with an 8.5-inch profile. That height fits most bunk beds and standard twin sheets.

Does the Serta Onyx come with a box spring?

No. The mattress is sold on its own. It works on a box spring, slatted frame or platform bed, and a platform base is the simplest option.

How long does the Serta Onyx warranty last?

One year, which is short for a mattress. Serta's main lines usually carry 10-year limited warranties, so treat this as a budget, shorter-life purchase.

When is the Serta Onyx Firm cheapest?

Budget mattresses like this one tend to drop during holiday sales and back-to-school events. Check the price history on this page before buying.

What do buyers say about the Serta Onyx Firm Twin Innerspring 8.5" Mattress?

Rated 4.4 out of 5 from 31 ratings.

Serta Onyx Firm Twin Innerspring 8.5" Mattress

4.4

Last price we saw

$179.95at Gardner-White Furniture, last seen Nov 4

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Our take on the Serta Onyx Firm Twin Innerspring 8.5" Mattress

The Serta Onyx is a firm twin innerspring mattress with an 8.5-inch profile, built as a basic, low-cost option for a guest room, bunk bed or kid's room. It uses a traditional coil support system rather than foam, so it sleeps firm and breathes better than all-foam beds at this price. The warranty is only 1 year, well short of the 10 years typical on Serta's main lines. It is a budget mattress, so expect a short service life and a simple build.