How to show the drop down attribute value using getData() method in magento 2?

Instead of getData() you need to use getAttributeText('attribute_code') for dropdown attributes. like

$_product->getAttributeText('material');

For multi-select try this :

$result = $_product->getResource()->getAttribute('material')->getFrontend()->getValue($_product);

To fetch value of attribute Use:

$this->getProduct()->getAttributeText('material');

Or

$this->getProduct()->getResource()->getAttributeRawValue($this->getProduct()->getId(),'material',$this->_storeManager->getStore()->getId());

You can get product attribute option values by below code

$_product->getAttributeText('material');

You can get multi select option values by

$_attributeValue = $block->getProduct()->getResource()->getAttribute('sizing_guidelines')->getFrontend()->getValue($block->getProduct());