A firm mattress is a type of mattress that provides a solid and supportive sleeping surface. It is designed to keep the spine properly aligned and reduce the risk of back pain by preventing the body from sinking too deep into the material. 

Here are some key points to consider about firm mattresses:

Benefits of a Firm Mattress:

1. **Spinal Alignment**: Helps maintain proper spinal alignment, which is crucial for preventing discomfort and pain.

2. **Support**: Provides excellent support for back and stomach sleepers, as it helps maintain a neutral spine position.

3. **Durability**: Often made with more resilient materials, firm mattresses may have a longer lifespan compared to softer ones.

4. **Better for Certain Sleepers**: Ideal for individuals who prefer less sinkage and like a more stable surface.

Who Might Prefer a Firm Mattress?

**Back Sleepers**: Benefit from the support as it prevents the lower back from sagging.

**Stomach Sleepers**: Helps maintain spinal alignment and prevent the hips from sinking too much.

**Heavier Individuals**: Often find firmer mattresses provide better support and prevent bottoming out.

Considerations:

**Personal Preference**: While some people enjoy the feeling of a firm mattress, others may find it uncomfortable if they prefer a softer sleeping surface.

**Material Composition**: Firmness can be influenced by materials used, including innerspring, memory foam, latex, or hybrids.

When choosing a firm mattress, it's essential to consider your sleeping position, body weight, and personal comfort preferences to ensure you select one that will promote a good night's sleep.