Mi colchón es duro, pero me ayuda con el dolor de espalda.

My mattress is hard, but it helps with my back pain.

Breakdown of Mi colchón es duro, pero me ayuda con el dolor de espalda.

• ser: to be
• con: with
• mi: my
• de: of

Questions & Answers about Mi colchón es duro, pero me ayuda con el dolor de espalda.

Why is ser used in es duro instead of estar?

In Spanish, ser describes inherent or long-lasting qualities, while estar indicates temporary states or locations. A mattress’s firmness is considered a permanent attribute, so you say es duro (it is firm) rather than está duro, which would imply it’s temporarily hard.

Why is the adjective duro masculine? Could I say dura?

Adjectives in Spanish must agree in gender and number with the nouns they modify. Colchón is masculine singular, so the adjective is duro (not dura). If you talked about a feminine noun (for example, almohada), you’d say almohada dura.

Why use pero instead of sino to connect the two clauses?

Pero simply introduces a contrast between two positive statements. Sino is used only when the first clause is negated and you want to correct or replace that negation. Here there’s no negation in Mi colchón es duro, so pero is the correct connector.

Could I replace pero with sin embargo?

Yes. Sin embargo also means “however” or “nevertheless,” but it’s a bit more formal. You’d typically write it with a semicolon or period before it:
Mi colchón es duro; sin embargo, me ayuda con el dolor de espalda.